Near-field optical head having tapered hole for guiding light beam

ABSTRACT

A near-field optical head for recording and reading-out information on and from a recording medium by utilizing near-field light produced from a very small aperture. The very small aperture is formed at an apex of a taper formed by an optical propagation member having a tip pointed toward a recording medium. A light introducing part is connected directly to the optical propagation member for propagating light along an optical path extending in a direction generally parallel to the recording medium. The optical propagation member is formed of a uniform dielectric layer in the light introducing part and inside of the taper. A light reflection layer reflects light propagated through the light introducing part toward the very small aperture.

TECHNICAL FIELD

The present invention relates to a near-field optical head for aninformation recording and reading-out apparatus which can record andread-out information with high density by reading-out structural oroptical information formed in very small area and recording informationto very small area by utilization of near-field light caused by opticalinteraction in the very small area.

BACKGROUND OF THE INVENTION

The information recording and reading-out apparatuses using light isadvancing toward increase of capacity and decrease of size, requiringrecording bit density increase. As a countermeasure there are studiesusing violet semiconductor lasers or SIL (Solid Immersion Lens). Withthese technologies, expectable improvement is at most nearly severaltimes the current recording density because of a problem withdiffraction limit of light. Contrary to this, there is an expectationfor an information recording and reading-out method utilizing near-fieldlight as a technology dealing with optical information in very smallarea exceeding the light diffraction limit.

This technology utilizes near-field light caused due to the interactionbetween a very small area and an optical aperture formed in a size lessthan a wavelength of light in a near-field optical head. This makes itpossible to deal with optical information in the region of less than alight wavelength as a limit in the conventional optical system. Theoptical information reading-out methods include a method of illuminatingscattering light onto a media surface to convert a greater part ofnear-field light localized at a very small mark into propagation lightthrough the interaction with the very small aperture (collection mode),and a method of illuminating near-field light produced through an verysmall aperture onto a media surface thereby detecting, by a separatelyprovided detector, scattering light converted through an interactionwith a microscopic concave-convex having information recorded on a mediasurface (illumination mode). Recording is made by illuminating thenear-field light produced from the very small aperture to a mediasurface thereby changing the form of a very small area on the media(heat mode record) or by changing the refractivity or transmissivity ina very small area (photon mode record). By using these near-fieldoptical heads having the optical very small aperture exceeding a lightdiffraction limit, recording bit density increase can be achievedexceeding beyond the conventional optical information recording andreading-out apparatuses.

In such situations, generally the recording and reading-out apparatusesutilizing near-field light are almost similar in structure to themagnetic disk apparatus, and employ a near-field optical head in placeof a magnetic head. The near-field optical head with an optical verysmall aperture mounted at a tip of a suspension arm is floated to agiven height by a flying head technology and accessed to an arbitrarydata mark existing on the disk. In order to follow up the near-fieldoptical head to high-speed rotation of the disk, a flexture function isprovided to stabilize the position coping with winding on the disk.

In the near-field optical head thus constructed, the method of supplyinglight to the aperture adopts means of connecting an optical fiber fromabove directly to the head or directly illuminating a laser providedabove a head onto the head.

Also, in place of the near-field optical head, an optical fiber probe orcantilever-type optical probe sharpened at an aperture part formed by anoptical fiber represented in a near-field optical microscope is used toachieve information recording and reading-out through an interaction bya tunnel current or interatomic force caused between a probe and a mediasurface of a scanning probe microscope while keeping a relative positionto the media.

Meanwhile, there is a proposal of using a planar probe having aninverted pyramid structured aperture formed in a silicon substrate byanisotropic etching. Light is incident from above and then reflectedupon the inverted conical pyramid thereby causing near-field lightthrough the aperture present at an apex thereof. This prove does nothave a sharpened tip as mentioned above and hence can be used as anoptical head suited for high speed recording and reading-out.

However, if light is incident with a structure connected an opticalfiber from above, an optical fiber structure is in connection betweenthe head and the arm to thereby preventing the head from moving freely.Thus, the head is difficult to control in position relative to diskmotion. Further, the head structured in large size makes it impossibleto maintain a distance between the disk and the aperture. This resultsin a situation that the output SN ratio from optical informationdepicted on the disk is lowered thus making it difficult to read andwrite signals. Meanwhile, the greater part of light attenuates beforereaching the aperture thus making it difficult to produce sufficientnear-field light from the aperture for implementing reading-out at highspeed. Furthermore, the structure having the upwardly extending fibersincreases the size of apparatus itself making difficult to reduce thesize and thickness thereof. Also, the optical fibers are inserted in andpositioned one by one on the head thus being short in massproducibility.

Meanwhile, where illuminating a signal by a laser arranged above thehead directly onto the head, there is a need of coping with high speedmovement of the head to synchronize light to be incident thereon. Thereis a necessity of separately providing a structure that moves responsiveto movement of the head thus encountering difficulty. Also, the separateprovision of such a structure increases the size of the apparatus itselfand the size reduction of the reading-out and recording apparatus isdifficult.

Furthermore, where keeping constant a distance to a media through theinteraction with a media surface by use of an optical fiber probe havingoptical fiber sharpened at its tip or a cantilever-type optical probesharpened at its tip, scanning should be made while controlling adistance to the media at all times. This requires a feedback apparatustherefor and making difficult to reduce the size of the recording andreading-out apparatus. Furthermore, there is also a problem in highspeed scanning because of a limitation of response speed of the feedbacksystem. Also, the tip-sharpened probe is not sufficient in mechanicalstrength and hence not suited for being arrayed. Also, the intensity ofnear-field light from the aperture is not sufficient due to light lossat a fiber tip. Also, the probe is manually fabricated one by one andlack in mass producibility.

Meanwhile, the planar probe requires light to be incident from abovethus posing a problem with apparatus size increase and massproducibility or a problem with reduction in flexture function asencountered in the above problem.

Furthermore, the probe aperture must be formed in a size smaller than awavelength of propagation light (laser light, etc.) in order to producenear-field light or scatter near-field light. It is however difficult tofabricate such a size (10 nano-meters to 200 nano-meters) of an apertureto an objective shape and size with accuracy and reproducibility.

For example, in the planar probe, etching is usually conducted formaking in a silicon substrate a very small aperture suited for producingor scattering near-field light. There are cases of encountering problemsconcerning silicon substrate quality or etch solution concentrationnonuniformity.

In concerned with silicon substrate quality in the former case, theperiodic existence of silicon crystalline surfaces are premised for amethod of forming a taper by anisotropic etching to open a holepenetrating the silicon substrate or a method of causing an aperture toappear by isotropically etching (etch-back) at an backside of thesilicon substrate forming a taper. This results in unetching in adirection or at a rate as intended in areas containing crystallinedefects or impurities, causing errors in the shape or size of a finallyavailable aperture.

Meanwhile, the problem with etch solution concentration nonuniformity inthe latter case means that there is more or less nonuniformity ofconcentration in an etch solution and such concentration nonuniformitycauses an area that etching advances at a high rate and that advances ata low rate on a silicon substrate, i.e. there appear areas different inetch rate resulting in causing errors in the shape or size of a finallyobtained aperture. Such a problem cannot be neglected particularly for acase where a multiplicity of planar probes are to be formed on a siliconwafer, thus posing a cause of incurring reduction of yield.

Accordingly, it is an object of the present invention to provide, in anear-field optical head having a very small aperture for producingnear-field light, a near-field optical head which is capable ofproducing near-field light sufficiently greater than the aperture andobtaining reading-out and recording with resolution, compact instructure and excellent in mass producibility and arraying with twodimensional arrangement, capable of stably recording and reading-out dueto movement following a media without hindering a flexure function,capable of recording and reading-out at high speed and being reduced insize and thickness.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, a near-field optical head of thepresent invention is characterized by comprising: a planar substrateformed penetrating through with an inverted conical or pyramidal holehaving an apex thereof made as the very small aperture; an opticalwaveguide formed on a surface opposite to a surface of the planarsubstrate forming the very small aperture; and a light reflection filmformed in the optical waveguide to bend an optical path.

Accordingly, once reflection of light upon the light reflection layermakes it possible to focus the light to a vicinity of the very smallaperture. This can increase the intensity of near field light producedfrom the aperture and provide a near field optical head high inmechanical strength, compact in structure and excellent in massproducibility.

Also, the near field optical head according to the invention ischaracterized in that the optical waveguide is also formed at an insideof the inverted conical or pyramidal hole.

Accordingly, the optical waveguide can be arranged close to the verysmall aperture, increasing the energy density of light illuminated tothe very small aperture and the intensity of near field light to beproduced from the aperture. Thus, a near field optical head is providedwhich is high in mechanical strength, compact in structure but excellentin mass producibility.

Also, the near field optical head according to the invention ischaracterized in that the optical waveguide is formed also on an innerside of the inverted conical, or pyramidal hole.

Accordingly, the optical waveguide can be arranged nearby the very smallaperture, increasing the energy density of light illuminated to the verysmall aperture and the intensity of near field light to be producedthrough the aperture. Thus, a near field optical head is provided whichis high in mechanical strength, compact in structure and excellent inmass producibility.

Also, the near field optical head according to the invention ischaracterized in that the inverted conical or pyramidal hole is formedby a plurality of slant surfaces different in slant degree. Furthermore,a feature is provided in that the plurality of slant surfaces a slantsurface having a slant degree smaller than a mean slant degree of theplurality of slant surfaces exists in a vicinity of the very smallaperture.

Accordingly, the structure having a moderate slant surface in thevicinity of the very small aperture can reduce the loss of lightpropagation in the vicinity of the aperture and increase the intensityof near field light to be produced from the aperture. Thus, a near fieldoptical head can be provided which is high in mechanical strength,compact in structure, excellent in mass producibility.

Also, the characterizing that in the plurality of slant surfaces atleast one slant surface has an angle of smaller than 55 degrees withrespect to the surface forming the very small aperture can reduce theloss of light propagation in the vicinity of the very small aperture andincrease the intensity of near field light to be produced from theaperture.

Also, the near field optical head according to the invention ischaracterized in that the inverted conical or pyramidal hole has atleast one of slant surface in a curved surface form. Otherwise, afeature is provided in that in a vicinity of the very small aperture, atleast one of the slant surface in a curved surface form decreases inslant degree as the aperture is approached.

Accordingly, the structure having a slant surface in the vicinity of thevery small aperture can reduce the loss of light propagation in thevicinity of the aperture and increase the intensity of near field lightto be produced from the aperture. Thus, a near field optical head can beprovided which is high in mechanical strength, compact in structure andexcellent in mass producibility.

Also, the near field optical head according to the invention ischaracterized in that the light reflection layer or the opticalwaveguide has a focusing function to the very small aperture or a lightcollimating function from the very small aperture (light scattered upondetecting near field light).

Accordingly, light can be focused to the very small aperture by aneffect of focusing function structured in the light reflection layer oroptical waveguide, increasing the intensity of near field light to beproduced from the aperture. Thus, a near field optical head is providedwhich is high in mechanical strength, compact in structure and excellentin mass producibility.

Also, the near field optical head is characterized to be provided whichcan efficiently propagate the light detected from the very smallaperture by an effect of optical collimating function structured in thelight reflection layer or optical waveguide.

Also, the near field optical head according to the invention ischaracterized in that the optical waveguide is structured by acombination of a clad and a core.

Accordingly, a near field optical head is provided high in lightpropagation efficiency by structuring the optical waveguide with a coreand a clad that are different in refractivity.

Also, the near field optical head according to the invention ischaracterized in that the planar substrate has a plurality of the verysmall apertures, the optical waveguide and the light reflection layerbeing formed on the surface opposite to the surface forming the verysmall aperture to guide light generated from at least one of lightsource to the plurality of very small apertures.

Accordingly, where using the near field optical head of the invention asan optical memory head, high-speed recording and reading-out ofinformation is feasible and a sufficient amount of light can be suppliedto a media without performing high-speed scanning of the probe. Thus, anear field optical head can be provided which is compact in structurebut excellent in mass producibility. Furthermore, an increased amount ofnear field light can be produced from the aperture thus making itpossible to input and output signals with high S/N ratio and manufacturea reliable apparatus.

Next, in manufacturing a near field optical head having a planarsubstrate formed penetrating through with an inverted conical orpyramidal hole having an apex thereof made as the very small aperture,an optical waveguide formed on a surface opposite to a surface formingthe very small aperture, and a light reflection layer formed in theoptical waveguide to bend an optical path, a method for manufacturing anear field optical head is characterized in that: the optical waveguideis formed laid on the planar substrate. Also, the optical waveguide ischaracterized to be formed bonded on the planar substrate.

Also, a method for manufacturing a near field optical head ischaracterized by including: a process of forming an inverted conical orpyramidal hole penetrating through the planar substrate to have an apexmade as the very small aperture; a process of laying an opticalwaveguide on a surface opposite to a surface forming the very smallaperture; a process of forming a light reflection layer in the opticalwaveguide in a manner bending an optical path.

Otherwise, an optical waveguide is characterized to be formed by aprocess of being bonded to a surface opposed to a surface forming thevery small aperture in place of the process of laying an opticalwaveguide on the surface opposed to the surface forming the very smallaperture.

Accordingly, the manufacturing method like this enables manufacture by asemiconductor manufacturing process using a photolithography technology.Thus, a near field optical head is provided which is high in mechanicalstrength, compact in structure and excellent in mass producibility.Also, a near field optical head and near field optical head array areprovided arrayed with a plurality of apertures formed on a samesubstrate.

Also, a method for manufacturing a near field optical head according tothe present invention is characterized by including: a process offorming an inverted conical or pyramidal hole penetrating through theplanar substrate to have an apex made as a first very small aperture; aprocess of forming a light reflection layer on a taper of the invertedcone or pyramidal hole, and forming a second very small aperture havinga size defined by a thickness of the light reflection layer and smallerthan the first very small aperture.

Accordingly, forming a comparatively large very small aperture (firstvery small aperture) on a planar substrate such as a silicon substratereduces variation in very small aperture due to etching or the like.Even for a very small aperture with variation, the film formingcomparatively easy in control on the inverted conical or pyramidal taperdefines a size of an actually-effective very small aperture (second verysmall aperture), hence providing a planar probe with yield.

Also, a method for manufacturing a near field optical head according tothe present invention is characterized by including: a process offorming an inverted conical or pyramidal hole penetrating through theplanar substrate to have an apex made as a first very small aperture; aprocess of forming a light reflection layer having a partly differentthickness on a taper of the inverted conical or pyramidal hole, andforming a second very small aperture having a shape defined by thethickness of the light reflection layer and different in shape from ashape of the first very small aperture.

Accordingly, forming a comparatively large very small aperture (firstvery small aperture) on a planar substrate such as a silicon substratereduces variation in very small aperture due to etching or the like.Even for a very small aperture with variation, the film formingcomparatively easy in control on the inverted conical or pyramidal taperdefines a size of an actually-effective very small aperture (second verysmall aperture), hence providing a planar probe with yield.

Also, a method for manufacturing a near field optical head of thepresent invention is characterized by including: a process of forming aninverted conical or pyramidal hole penetrating through the planarsubstrate to have an apex made as a first very small aperture; a processof forming in the planar substrate a light reflection film on a surfaceincluding the first very small aperture, and forming a second very smallaperture having a size defined by a thickness of the light reflectionfilm and smaller than the first very small aperture.

Accordingly, forming a comparatively large very small aperture (firstvery small aperture) on a planar substrate such as a silicon substratereduces variation in very small aperture due to etching or the like.Even for a very small aperture with variation, the film formingcomparatively easy in control on a backside of the planar substrate (ona surface including the first very small aperture) defines a size of anactually-effective very small aperture (second very small aperture),hence providing a planar probe with yield.

Also, a method for manufacturing a near field optical head according tothe present invention is characterized by including: a process offorming an inverted conical or pyramidal hole penetrating through theplanar substrate to have an apex made as a first very small aperture; aprocess of forming an oxide film on a surface of the planar substrateincluding a taper of the inverted conical or pyramidal hole, and forminga second very small aperture having a size defined by a thickness of theoxide film and smaller than the first very small aperture.

Also, a method is characterized by including: a process of forming aninverted conical or pyramidal hole penetrating through the planarsubstrate to have an apex made as a first very small aperture; a processof performing ion implant to a surface of the planar substrate includinga taper of the inverted conical or pyramidal hole, and forming a secondvery small aperture having a size defined by a thickness expanded due tothe ion implant and smaller than the first very small aperture.

Accordingly, a very small aperture (first very small aperture) is formedgreater than a target size or shape in a planar substrate such as asilicon substrate to perform thermal oxidation or ion implant on or to asurface including the very small aperture taper whereby an expanded partdefines a size and shape of a very small aperture (second very smallaperture) to actually produce near field light. This accordingly solvesthe problem with deviation in microscopically forming an aperture in asilicon substrate through etching or the like by thermal oxidation orion implant comparatively easy to control. Thus, a planar probe can beobtained with yield.

Also, in order to achieve the above object, a near field optical headaccording to the present invention comprises: a planar substrate formedthrough with an inverted conical or pyramidal hole to have an apexthereof made as a very small aperture; an optical waveguide laid on anopposite surface of the planar substrate to a surface forming the verysmall aperture and on an inside of the inverted conical or pyramidalhole; a tip sharpened microscopic protrusion formed by one part of theoptical waveguide and protruding from the very small aperture of theplanar substrate.

Also, a light reflection layer for reflecting light is formed on aperiphery of the optical waveguide in an area excepting the protrusion.

Accordingly, the structure of the optical waveguide makes it possible tosupply an increased amount of light to the protrusion to produce nearfield light. Further, the reflection of light by the light reflectionlayer can supply an increased amount of light toward a tip (protrusion)of the optical waveguide. Consequently, the near field light caused atthe microscopic protrusion formed at the tip can be increased inintensity. Thus, a near field optical head is provided which is high inmechanical strength, compact in structure but excellent in massproducibility.

Also, in the near field optical head according to the invention, themicroscopic protrusion is characterized in an square pyramid form.

Accordingly, at the tip the region that the optical waveguide width issmaller in dimension than a wavelength of light is made narrow therebyincreasing the intensity of near field light produced from theprotrusion and enabling observation with a resolution corresponding to aradius of curvature at the tip of the sharpened protrusion.

Also, a near field optical head according to the invention, the invertedconical or pyramid hole is characterized to be formed by a plurality ofslant surfaces different in slant degree.

Accordingly, by making the optical waveguide in a structure having amoderate curved surface form, the loss of light propagation can betotally reduced at the curved surface thus increasing the intensity ofnear field light created from the protrusion.

Also, a near field optical head according to the invention, the opticalwaveguide is characterized to be formed by a combination of a core and aclad.

Accordingly, by structuring the optical waveguide with differentrefractivities of a core and a clad, a near field optical head can beprovided which is high in light propagation efficiency.

Also, in the near field optical head according to the invention, theplanar substrate is characterized having a plurality of microscopicprotrusion, and the optical waveguide and the light reflection layerbeing formed to guide light emitted from at least one light sourcetoward the plurality of microscopic protrusion.

Accordingly, by making a structure having the optical waveguide andlight reflection layer, light can be propagated with efficiency to themicroscopic protrusion located at a tip of the optical waveguide.Further, by making a structure narrowed in the region that the opticalwaveguide width at the protrusion is smaller in dimension than awavelength of light, the near field light produced from the protrusioncan be increased in intensity. Thus, a near field optical head isprovided that observation is possible with a resolution corresponding toa radius of curvature at the tip of the sharpened protrusion. Also, anear field optical head is provided which is high in mechanicalstrength, compact in structure and excellent in mass producibility.Two-dimensionally scanning such a probe makes it possible to processtotally at high speed an near field optical image with resolution. Also,making in array provides an optical probe capable of recording andreading-out information at high speed without requiring high speedscanning.

Next, in a method for manufacturing a near field optical head ischaracterized by including: a process of forming an inverted conical orpyramidal hole in a planar substrate; a process of laying an opticalwaveguide on the planar substrate including an inside of the invertedconical or pyramidal hole; a process of forming a microscopic protrusionfor light detection or illumination on an opposite surface of the planarsubstrate to the inverted conical or pyramidal hole; and a process offorming a light reflection layer in a manner bending an optical path.

Also, in manufacturing a near field optical head comprising a planarsubstrate formed through with an inverted conical or pyramidal hole tohave an apex thereof made as a very small aperture, an optical waveguidelaid on an opposite surface of the planar substrate to a surface formingthe very small aperture and on an inside of the inverted conical orpyramidal hole, a tip sharpened microscopic protrusion formed by onepart of the optical waveguide and protruding from the very smallaperture of the planar substrate, a method for manufacturing a nearfield optical head is characterized in that: the optical waveguide andthe light reflection layer are formed by laying on the planar substrate.

Accordingly, such a manufacturing method enables manufacture by asemiconductor manufacturing process using photolithography techniquethus providing a near field optical head compact in structure, well inreproducibility and excellent in mass producibility. Also, a near fieldoptical head can be provided which is arrayed forming a plurality ofapertures on a same substrate.

Furthermore, in order to achieve the above object, a near field opticalhead for recording and/or reading-out information of a recording mediautilizing near field light, a near field optical head is characterizedby comprising: an optical waveguide comprising a first clad formedthrough with at least one inverted conical or pyramidal hole to have anapex thereof made as a very small aperture, a core formed in a depthdirection along a side surface of the inverted conical or pyramidalhole, and a second clad formed in a manner cooperating with the firstclad to clamp the core; and a first reflection film formed on one endsurface of the optical waveguide.

Also, the light incident on the incident end of the core propagatesthrough the core and then reflected by the first reflection film towardthe very small aperture. The reflection light propagates through thecore formed in the inverted conical or pyramidal hole and then emittedthrough the very small aperture thereby producing near field light in avicinity of the very small aperture. In this manner, the structure usingthe optical waveguide in place of a conventional optical fiber enablesto reduce size and weight.

Also, a second reflection film is characterized to be formed on anbackside of the first clad and having a microscopic diameter hole in aposition corresponding to the very small aperture.

Accordingly, the formation of the second reflection film eliminatesleakage of core leak light to an outside of the optical waveguide thuseffectively narrowing a light illumination range on a recording surfaceof a recording medium.

Also, the one end surface of the optical waveguide is characterized tobe made in a curved surface.

Accordingly, the curved surface at one end surface of the opticalwaveguide causes the first reflection film to acts as a concave mirrorso that the laser light propagated through the core is focused by thefirst reflection film and reflected toward the very small aperture.

Also, in a near field optical head for recording and/or reading-outinformation of a recording media utilizing near field light, a nearfield optical head is characterized by comprising: an optical waveguidecomprising a clad formed through with at least one inverted conical orpyramidal hole to have an apex thereof made as a very small aperture anda core formed in a depth direction along a side surface of the invertedconical or pyramidal hole; a reflection film formed on one end surfaceof the optical waveguide; a substrate bonded on the core and having arefractivity different from a refractivity of the core.

Accordingly, because the substrate is bonded on the core and has areflectivity different from the reflectivity of the core, it serves as aclad for the optical waveguide.

Also, in a method for manufacturing a near field optical head forrecording and/or reading-out information to and from recording mediumutilizing near field light, a method for manufacturing near fieldoptical head is characterized by comprising: a first process of forminga first clad on a substrate; a second process of forming in the firstclad at least one inverted conical or pyramidal hole such that an apexthereof is made as a very small aperture; a third process of forming acore in a depth direction along the first clad and the side surface ofthe inverted conical or pyramidal hole; a fourth process of forming asecond clad in a manner of cooperating with the first clad to clamp thecore; a fifth process of forming a reflection film on one end surface ofan optical waveguide formed by the first clad, the core and the secondclad; and a sixth process of removing the substrate.

Accordingly, in the first process a first clad is formed in thesubstrate. In the second process an inverted conical or pyramidal holeis formed in the first clad such that an apex thereof is made as a verysmall aperture. In the third process a core is formed in a depthdirection along the first clad and along a side surface of the invertedconical or pyramidal hole. Furthermore, in the fourth process a secondclad is formed in a manner cooperating with the first clad to clamp thecore. In the fifth process a reflection film is formed on one endsurface of the optical waveguide. In the final sixth process thesubstrate is removed thereby manufacturing a near field optical headhaving an optical waveguide.

Also, in order to achieve the above object, a near field optical headaccording to the present invention is characterized by comprising: avery small aperture formed at an apex of a taper formed by an opticalpropagation member having a tip sharpened toward a recording medium; alight introducing part for propagating light generally in a paralleldirection with the recording medium; and a light reflection layer forreflecting light propagated through the light introducing part towardthe very small aperture.

Accordingly, in the case that light is incident from above to a nearfield optical head, the near field optical head is introduced with lightin a direction parallel to a recording medium thereby making it possibleto reduce the size and thickness of the overall apparatus against theproblem of increasing the apparatus structure. Furthermore, it ispossible to follow up the winding on the recording medium and hence keepat all times a constant relative position to the recording medium.Consequently, stable near field light can be supplied at all times tothe recording medium. Thus, a near field optical head can bemanufactured which is high in reliability.

Furthermore, in the near field optical head according to the invention,the taper is characterized having at least one part structured by acombination of a plurality of tapers different in angle of apex spread.In particular, the plurality of tapers has, in a vicinity of the verysmall aperture, a taper having an angle of spread greater than a meanangle of spread of the plurality of tapers. Otherwise, the taper has acurved surfaced taper in at least one part thereof. In particular, atleast one of the curved surfaced taper increases in angle of spread inthe vicinity of the very small aperture as the aperture is approached.

Accordingly, although the intensity of light largely attenuates in aregion where the light propagation member is smaller in width than awavelength of light, the structure made narrow in this region makes itpossible to produce an increased amount of near field light from thevery small aperture. This results in dealing with signals high in S/Nratio in recording and reading-out information to and from a recordingmedium thus providing a near field optical head high in reliability.Also, even where the amount of light is less at the laser light source,high conversion efficiency to near field light enables supply of nearfield light required for a recording medium. Accordingly, power savingis feasible at the laser light source. Thus, an information reading-outand recording apparatus is provided which can be driven with low powerconsumption and at low voltage.

Otherwise, in the near field optical head according to the invention,the taper is characterized to be asymmetric in shape about a center axisof the taper passing the apex.

Accordingly, a distribution of near field light under the influence ofthe featured shape is illuminated to a recording medium therebyeffectively determining an illumination range and enabling informationrecording and reading-out in a manner suited for purposes.

Also, in the near field optical head according to the invention, thelight propagation member in at least one part is characterized to be ofdielectric.

Accordingly, the refractivity of the light propagation member is greaterthan that of air. Where viewing the aperture from the propagation light,the apparent size of the aperture is in a size of times therefractivity. Where a wavelength in propagation be same, thetransmissivity improves at the aperture. Otherwise, forming arefractivity distribution or curved surface form on the dielectricprovides a function as a lens. By aligning its focus to the aperture,greater near field light can be produced.

Otherwise, the light propagation member in at least one part ischaracterized to be of air.

Because an aperture can be fabricated by opening a hole by etching, theprocess can be simplified with manufacture at low cost.

Also, in the near field optical head according to the invention, thetaper in at least one part is characterized to be covered by metal.

Accordingly, the amount of propagation light to the aperture isincreased due to reflection of light upon the taper metal therebyproducing increased amount of near field light.

Also, in the near field optical head according to the invention, thetaper in at least one part is characterized to be covered by dielectric.Otherwise, the taper in at least one part is characterized to be coveredby dielectric having a refractivity smaller than a refractivity ofdielectric constituting the light propagation member.

Accordingly, the amount of propagation light to the aperture isincreased due to reflection of light upon the taper metal therebyproducing increased amount of near field light.

Also, in the near field optical head according to the invention, aprotrusion protruded from the very small aperture is characterized to beprovided. Furthermore, the protrusion in at least one part ischaracterized to be dielectric.

Accordingly, the shape of the projection causes a featured spatialdistribution of near field light so that an illumination range can bedetermined by utilizing the same.

Also, the protrusion at least in one part is characterized to be coveredby metal.

Accordingly, the near field light caused on a recording medium surfacecan be scattered over a range dependent upon the protrusion shape thuseffectively determining a scattering range.

Also, the protrusion is characterized to be in a conical or pyramidalform.

Accordingly, high resolution information recording and reading-out arepossible by the near field light caused around the sharpened tip.

Also, in the near field optical head according to the invention, arelative position to the recording medium is characterized to be keptconstant by a floating force undergone from a side of the recordingmedium and a load weight applied toward the recording medium.Furthermore, the floating force is characterized to be an air pressurecaused due to high speed motion of the recording medium. Otherwise, thefloating force is characterized to be due to a pressure of a liquidapplied in a constant thickness on a surface, of the recording medium.

Also, a relative position to the recording medium is characterized to bekept constant by controlling an electric interaction caused with therecording medium. Otherwise, a relative position to the recording mediumis characterized to be kept constant by controlling an interatomic forceinteraction caused with the recording medium.

Accordingly, the spacing to a recording medium can be kept constant andin a fully proximate state while reading-out from the recording mediumat high speed, thereby achieving high speed processing of microscopicbits. Furthermore, realized is size reduction of the apparatusstructure.

Also, in the near field optical head according to the invention, aslider structure is characterized to be provided in a surface opposed tothe recording medium.

Accordingly, stable floating of the near field optical head is obtained.Because constant supply of near field light is possible on a recordingmedium surface, an information recording and reading-out apparatus lowin error rate but high in reliability can be manufactured.

Also, in the near field optical head according to the invention, thevery small aperture is characterized to be formed in a slider surface.Furthermore, a spacing between the recording medium and the very smallaperture is characterized to be nearly same as a spacing between therecording medium and the slider. Also, the taper and the sliderstructure are provided in proximity with. Otherwise, the sliderstructure is characterized to be arranged in a manner surrounding by 180degrees over a periphery of the taper.

Accordingly, the structure that the damage due to contact with arecording medium is reduced while making close the distance between thevery small aperture and the media makes it possible to manufacture anear field optical head which is hardly broken and strong, reliable andhigh in signal SN ratio.

Also, the slider structure in at least one part is characterized to bedielectric.

Otherwise, the slider structure in at least one part is characterized tobe metal.

Accordingly, the slider in a surface can be worked smooth to a statealmost free of concave-convex, allowing for proximity to a media withless contact therewith. Also, adoption in a silicon process is possiblethus improving mass producibility.

Also, in the near field optical head according to the invention, thelight reflection layer in at least one part is metal. Furthermore, thelight reflection layer is characterized to have a focusing function tofocus the light reflected toward the very small aperture. Also, thelight reflection layer is characterized to have a light reflectingsurface in a concave surface. Otherwise, the light reflection layer ofthe near field optical head according to claim 61 is characterized tohave a light reflecting surface having a grating structure.

Accordingly, the light propagated parallel with a recording medium canbe reflected toward the aperture. The illumination from above makes itpossible to produce an increased amount of near field light from theaperture due to an effect of reflection upon the taper. Also, theprovision of the focusing function increases the collection of light tothe aperture, thus producing increased amount of near field light.

Also, in the near field optical head according to the invention, thelight reflection layer is characterized to be formed by working one partof the light introducing part and laying on a worked surface thereof.

Accordingly, because of the process allowing for manufacture by amicro-machining process using silicon or the like, the structure issuited for mass production and can be manufactured at low cost. Also,because of working a fiber or optical waveguide itself, there is lesspropagation loss. Such as loss due to refractivity change, thusimproving supply amount of light to the aperture.

Also, in the near field optical head according to the invention, thelight reflection layer is characterized to be formed by laying on aslant surface formed at a constant angle as determined by a planarorientation due to chemical etching. Furthermore, the slant surfacehaving a constant angle as determined by a planar orientation ischaracterized to be in a (111) plane formed in (100) planed singlecrystal silicon. Otherwise, the light reflection layer is characterizedto have a reflecting direction of light of approximately 70 degrees withrespect to a propagation direction in the light introducing part.

Accordingly, the micro-machining process manufacture provides a constantangle thereby supplying a constant amount of light at all times to theaperture. Also, the light propagated through the light introducing partreaches the aperture through once reflection. Thus, the amount ofattenuation light due to reflection can be reduced as compared to thecase of reaching the aperture through twice or trice reflections. Also,the adaptation to a silicon process enables to manufacture a near fieldoptical head excellent in size reduction/mass producibility.

Also, in the near field optical head according to the invention, thelight introducing part in at least one part is characterized to bedielectric. Otherwise, the light introducing part in at least one partis characterized to be air.

Accordingly, the loss in propagation is reduced to extremely low and thelight from the laser light source can be sufficiently supplied to thelight reflection layer.

Furthermore, the light introducing part in at least one part ischaracterized to be an optical fiber. Also, the light introducing partin at least one part is characterized to include a combination of a corerelatively high in refractivity and a clad relatively low inrefractivity.

Accordingly, the light from the laser light source can be suppliedpositively to the light reflection layer in a very small area withoutbeing scattered and attenuated. Also, it is possible to set an arbitraryillumination spot and positively supply light to the aperture.

Furthermore, in the near field optical head according to the invention,the light introducing part in at least one part is characterized to,have a focusing function to focus light to be propagated to the verysmall aperture. Otherwise, the light introducing part is characterizedto have a vertical surface to a light propagation direction having atleast one part made in a convex form. Also, the light introducing partin at least one part is characterized to have a grating structure. Also,the light introducing part in at least one part is characterized to havea gradient of refractivity having a refractivity different stepwise.

Accordingly, by setting the focusing function to make a microscopic spotaligned to the aperture, an increased amount of near field light can beproduced from the aperture. Thus, a near field optical head can beformed that is high in signal SN ratio.

Furthermore, in the near field optical head according to the invention,the taper in at least one part is characterized to be provided with afocus functioning member having a focusing function to focus light tothe very small aperture. Otherwise, a focus functioning member having afocusing function to focus light to the very small aperture ischaracterized to be provided in at least one part of an optical pathbetween the light reflection layer and the taper. Also, a focusfunctioning member having a focusing function to focus light to the verysmall aperture is characterized to be provided in at least one part ofthe light reflection layer. Also, a focus functioning member having afocusing function to focus light to the very small aperture ischaracterized to be provided in at least one part of the lightintroducing part.

Accordingly, against a problem that microscopic movement in the headcauses a focus point to deviate from the aperture resulting in increasedvariation in recording and reading-out signals in the case where lightis illuminated to the aperture from above the near field optical head,the provision of the focusing function within the near field opticalhead provides focus setting to the aperture thus allowing for recordingand reading-out in a state of always focusing to the apertureirrespectively of head movement. Thus, because a sufficient amount ofnear field light can be produced at all times, an information recordingand reading-out apparatus can be manufactured which is high in SN ratioand reliability.

Furthermore, the focus functioning member in at least one part ischaracterize to be dielectric. Also, the focus functioning member ischaracterized to have a vertical surface to a light propagationdirection having at least one part made in convex form. Furthermore, thefocus functioning member is characterized to be spherical. Also, thefocus functioning member in at least one part is characterized to have arefractive gradient having a refractivity different stepwise. Also, thefocus functioning member in at least one part is characterized to have agrating structure.

Accordingly, the lens effect of them makes possible to produce asufficiently high near field light from the aperture. Thus, aninformation recording and reading-out apparatus can be manufacturedwhich is high in SN ratio and reliability. Also, even where the lightamount of the laser light source is reduced, an increased amount of nearfield light can be produced from the aperture. Thus, an informationrecording and reading-out apparatus can be manufactured which is low inpower consumption and voltage drive.

Also, in the near field optical head according to the invention, thevery small aperture and the light reflection layer are characterized tobe provided in proximity with. Otherwise, a distance between the verysmall aperture and the light reflection layer is characterized to be 20μm or less.

Accordingly, even where the light reflected by the light reflectionlayer and propagated toward the aperture is scattering light, theaperture if provided nearby the light reflection layer making a spotsize of light illuminated to the aperture to nearly a size of a spotsize on the reflection surface. Thus, high energy density light isilluminated to the aperture. Accordingly, near field light can beproduced greater than the aperture, enabling to form a reliable nearfield optical head.

Also, in the near field optical head according to the invention, anapertured substrate having the very small aperture is characterized tobe provided on a surface opposed to the recording medium. On theapertured substrate, the light reflection layer is characterized to belaid and formed on an opposite surface forming the very small apertureof the apertured substrate. Otherwise, the light reflection layer ischaracterized to be bonded and formed on an opposite surface forming thevery small aperture of the apertured substrate. Also, the lightreflection layer is characterized to be laid and formed in a surfaceforming the very small aperture of the apertured substrate. Otherwise,the light introducing part is characterized to be laid and formed on anopposite surface forming the very small aperture of the aperturedsubstrate. Also, the light introducing part is characterized to bebonded and formed on an opposite surface forming the very small apertureof the apertured substrate. Otherwise, the light introducing part ischaracterize to be laid and formed in a surface forming the very smallaperture of the apertured substrate. Also, the light focus functioningmember is characterized to be laid and formed on an opposite surfaceforming the very small aperture of the apertured substrate. Otherwise,the light focus functioning member is characterized to be bonded andformed on an opposite surface forming the very small aperture of theapertured substrate.

Accordingly, where forming devices having respective functions by layingor bonding on a top surface of the substrate, manufacture is possiblewith using micro-machining such as a silicon process. This allows forsize reduction for the near field optical head and further theinformation recording and reading-out apparatus itself. Furthermore, thesize reduction of the near field optical head enables further proximityto a recording medium. This allows for reading out and writing in ofmicroscopic bits with utilization of the very small aperture put inproximity. Thus, a high density information recording and reading-outapparatus is made feasible to manufacture.

Also, in manufacturing a near field optical head having a very smallaperture formed at an apex of a taper formed by a light propagationmember sharpened at a tip toward a recording medium, a light introducingpart for propagating light generally in a parallel direction with therecording medium, a light reflection layer for reflecting lightpropagated through the light introducing part toward the very smallaperture, and a focus functioning member provided on an optical pathbetween the light reflection layer and the taper and having a convexform in at least one part of a surface vertical to a direction of lightpropagation or a focus functioning member different stepwise inrefractivity, a method for manufacturing a near field optical headaccording to the present invention is characterized in that:

the focus functioning member is formed by working a surface thereof bychemical etching.

Otherwise, the focus functioning member is characterized to be formed byexchanging ions from one part of a surface thereof.

Otherwise, the focus functioning member is characterized to be formed byexchanging ions from one part of a surface thereof.

Otherwise, the focus functioning member is characterized to be formed bysetting with UV radiation a liquid having a curved surface due to asurface tension.

Otherwise, the focus functioning member is characterized to be formed bythermosetting a liquid having a curved surface due to a surface tension.

Also, in manufacturing a near field optical head having a very smallaperture formed at an apex of a taper formed by a light propagationmember sharpened at a tip toward a recording medium, a light introducingpart for propagating light generally in a parallel direction with therecording medium, a light reflection layer for reflecting lightpropagated through the light introducing part toward the very smallaperture, and a metal covering the taper, a method for manufacturing anear field optical head is characterized in that:

the taper is formed by conducting surface working using chemicalreaction.

Otherwise, the very small aperture is characterized to be formed byplastically deforming the metal in a vicinity of an apex of the taperwith using a material harder than the metal.

Also, a method for manufacturing a near field optical head according tothe present invention is characterized by including: process of formingin a surface opposed to a recording medium a taper of a dielectricsharpened at a tip toward the recording medium; a process of laying ametal film on a periphery of the taper; a process of working a metalfilm at a tip of the taper to thereby form a very small aperture; aprocess of working an opposite surface forming the very small apertureto thereby form a convex form or a process of performing ion exchange onan opposite surface forming the very small aperture to thereby form aconvex form or a process of applying and UV-set a liquid to an oppositesurface forming the very small aperture or a process of performing ionexchange on an opposite surface forming the very small aperture tothereby form a refractivity gradient different in refractivity; and aprocess of bonding onto the convex-worked surface or surface forming arefractive gradient a light introducing part for propagating lightgenerally in a direction parallel with a recording medium and a lightreflection layer for reflecting light propagated through the lightintroducing part toward the very small aperture.

Otherwise, characterized to be included are: a process of forming in asurface opposed to a recording medium a taper of a dielectric sharpenedat a tip toward the recording medium; a process of laying a metal filmon a periphery of the taper; a process of working a metal film at a tipof the taper to thereby form a very small aperture; a process of bondinga spherical lens on an opposite surface forming the very small aperture;and a process of bonding onto a surface of the spherical lens a lightintroducing part for propagating light generally in a direction parallelwith a recording medium and a light reflection layer for reflectinglight propagated through the light introducing part toward the verysmall aperture.

Also, a method for manufacturing a near field optical head according tothe present invention is characterized by including: a process offorming in a surface opposed to a recording medium a taper of airsharpened at a tip toward the recording medium and a first very smallaperture at an apex thereof; a process of laying a metal film on aperiphery of the taper to form a second very small aperture; a processof bonding a dielectric having a surface vertical to a direction oflight propagation having a part formed in a convex form or a dielectrichaving a refractivity gradient different in refractivity or a sphericallens onto an opposite surface forming the second very small aperture;and a process of bonding onto a surface of the dielectric a lightintroducing part for propagating light generally in a direction parallelwith a recording medium and a light reflection layer for reflectinglight propagated through the light introducing part toward the verysmall aperture.

Also, characterized to be included are: a process of forming in asurface opposed to a recording medium a taper of air sharpened at a tiptoward the recording medium and a first very small aperture at an apexthereof; a process of laying a metal film on a periphery of the taper toform a second very small aperture; a process of applying and UV-set aliquid over an opposite surface forming the second very small apertureto thereby form a convex form; and a process of bonding onto a surfaceformed in the convex form a light introducing part for propagating lightgenerally in a direction parallel with a recording medium and a lightreflection layer for reflecting light propagated through the lightintroducing part toward the very small aperture.

Also, in manufacturing a near field optical head having a very smallaperture formed at an apex of a taper formed by a light propagationmember sharpened at a tip toward a recording medium, a light introducingpart for propagating light generally in a parallel direction with therecording medium, a light reflection layer for reflecting lightpropagated through the light introducing part toward the very smallaperture, and an apertured substrate having a very small aperture on asurface opposed to the recording medium, a method for manufacturing anear field optical head according to the present invention ischaracterized in that: the very small aperture, the light introducingpart and the light reflection layer are formed by working a materiallaid on an opposed surface of the apertured substrate to the recordingmedium.

Also, characterized to be included are: a process of forming by usingchemical reaction a slant surface having a constant angle defined by aplanar orientation on a surface opposed to the recording medium; aprocess of forming a light reflection layer by laying a metal on theslant surface; a process of forming a light introducing part by laying adielectric on a top surface of the light reflection layer; a process ofplanarize the dielectric layered; a process of working a part of thedielectric into a taper sharpened toward the recording medium by usingchemical reaction; a process of laying a metal film on a top surface ofthe taper; and a process of working the metal film at an apex of thetaper to thereby form a very small aperture.

Accordingly, the adoption of these manufacturing method can cope with amicro-machining process such as a silicon process thus realizingsmall-sized and compact structure of a near field optical head. Also,the stable manufacture process allows for manufacturing of a precisefocus functioning member and hence forming a near field optical headhigh in reliability and good in reproducibility. Also, because ofprocessable in batch, a near field optical head can be manufactured atlow cost by mass producibility. Also, by the use of such a manufacturingprocess, near field light can be stably produced from the very smallaperture in a manner coping with high speed movement of a recordingmedium while being put proximity thereto with a distance to therecording medium kept constant at all times, thereby enabling supply ofa near field optical head which can read-out or record, with high SNratio, microscopic bit information at high speed.

Also, in the near field optical head according to the invention, thevery small aperture is characterized by provided in plurality of number,and the light introducing part and the light reflection layer beingformed to guide light emitted from at least one light source toward adirection of the plurality of very small apertures.

Accordingly, by two-dimensionally scanning the near field optical headand simultaneously processing a plurality of ones of microscopic bitinformation at a plurality of very small apertures, it is possible toimplement processing entirely at high speed without the necessity ofincreasing the speed of rotation of the recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an optical storing and reading-outapparatus according to Embodiment 1 of the present invention;

FIG. 2 is a media-side schematic view of a near-field optical headaccording to Embodiment 1 of the invention;

FIG. 3 is a media-side schematic view of the near-field optical headaccording to Embodiment 1 of the invention;

FIG. 4 is a media-side schematic view of the near-field optical headaccording to Embodiment 1 of the invention;

FIG. 5 is a sectional view showing one part of the near-field opticalhead according to Embodiment 1 of the invention;

FIGS. 6A and 6B are explanatory views showing a manufacturing processfor the near-field optical head shown in FIG. 5, FIG. 6A illustratingthe shape as viewed from the side and FIG. 6B illustrating the shape asviewed from the top;

FIG. 7 is an explanatory view showing an array of the near-field opticalheads according to Embodiment 1 of the invention;

FIG. 8 is a sectional view showing one part of a near-field optical headaccording to Embodiment 2 of the invention;

FIG. 9 is a sectional view showing one part of a silicon substrateconstituting for a near-field optical head according to Embodiment 3 ofthe invention;

FIGS. 10A and 10B are explanatory views showing a manufacturing processon a silicon substrate constituting for the near-field optical headshown in FIG. 9, FIG. 10A illustrating the shape as viewed from the sideand FIG. 10B illustrating the shape as viewed from the top.

FIG. 11 is a sectional view showing one part of a silicon substrateconstituting for a near-field optical head according to Embodiment 4 ofthe invention;

FIG. 12 is an explanatory view showing one example of a manufacturingprocess on a silicon substrate constituting for the near-field opticalhead shown in FIG. 11.

FIG. 13 is an explanatory view showing one example of a manufacturingprocess on a silicon substrate constituting for the near-field opticalhead shown in FIG. 11.

FIG. 14 is a sectional view of an aperture formed in a silicon substratein a manufacturing method for a near-field optical head according toEmbodiment 5 of the invention;

FIG. 15 is a sectional view of an aperture having a film formed on ataper in Embodiment 5 of the invention;

FIGS. 16A and 16B are top views of a very small aperture aftermodification in Embodiment 5;

FIG. 17 is a figure showing a relationship between a film thickness tand a protrusion amount Δr where a film is formed on the taper inEmbodiment 5;

FIG. 18 is a figure showing a relationship between a film thickness tand a height deviation Δz from a bottom of a maximum protruding point inEmbodiment 5;

FIG. 19 is an explanatory view showing a manner of controlling the sizeor shape of a very small aperture formed in a planar substrate accordingto Embodiment 5 of the invention;

FIG. 20 is an explanatory view showing a manner of controlling the sizeor shape of a very small aperture formed in a planar substrate accordingto Embodiment 6 of the invention;

FIG. 21 is a sectional view showing one part of a near-field opticalhead according to Embodiment 7 of the invention;

FIG. 22 is an explanatory view showing a manufacturing process for thenear-field optical head shown in FIG. 21;

FIG. 23 is an explanatory view showing an array of the near-fieldoptical heads having an optical waveguide according to Embodiment 7 ofthe invention;

FIG. 24 is a sectional view showing one part of a near-field opticalhead according to Embodiment 8 of the invention;

FIG. 25 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 9 of the invention;

FIGS. 26A-26F are side sectional views for explaining a manufacturingmethod for a near-field optical head according to Embodiment 9 of theinvention;

FIG. 27 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 10 of the invention;

FIG. 28 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 11 of the invention;

FIG. 29 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 12 of the invention;

FIG. 30 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 13 of the invention;

FIG. 31 is a side sectional view showing one part of a near-fieldoptical head according to Embodiment 13 of the invention;

FIG. 32 is a side sectional view showing one part of the near-fieldoptical head according to Embodiment 13 of the invention;

FIG. 33 is a side sectional view showing one part of the near-fieldoptical head according to Embodiment 13 of the invention;

FIG. 34 is a side sectional view showing one part of the near-fieldoptical head according to Embodiment 13 of the invention;

FIG. 35 is a side sectional view for explaining a manufacturing methodfor one part of the near-field optical head according to Embodiment 13of the invention;

FIG. 36 is a side sectional view for explaining a manufacturing methodfor one part of the near-field optical head according to Embodiment 13of the invention;

FIG. 37 is a side sectional view for explaining a manufacturing methodfor one part of the near-field optical head according to Embodiment 13of the invention;

FIG. 38 is a side sectional view for explaining a manufacturing methodfor one part of the near-field optical head according to Embodiment 13of the invention;

FIG. 39 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 14 of the invention;

FIG. 40 is a side sectional view for explaining a manufacturing methodfor one part of a near-field optical head according to Embodiment 14 ofthe invention;

FIG. 41 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 15 of the invention;

FIG. 42 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 16 of the invention;

FIG. 43 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 16 of the invention;

FIG. 44 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 17 of the invention;

FIG. 45 is a side sectional view showing a structure of a near-fieldoptical head according to Embodiment 18 of the invention;

FIG. 46 is an explanatory view showing a manufacturing process for anear-field optical head in Embodiment 18 shown in FIG. 45.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder, embodiments of near-field optical heads according to thepresent invention will be explained in detail with reference to thedrawings. It should be noted that the invention is never limited to bythe embodiments.

Embodiment 1

FIG. 1 illustrates a schematic view of an example of an optical storingand reading-out apparatus according to Embodiment 1 of the invention. Anear-field optical head 102 is arranged over a disk 101 (media) rotatingat high speed to keep a constant distance to the disk 101 due to afloating force undergone by fluid motion caused by the rotation and aload weight of an arm 103. The way of keeping the distance to the disk101 may adopt a method to control the interaction, such as tunnelcurrent or interatomic force, caused between the near-field optical head102 and the media surface. The near-field optical head 102 is supportedat a tip of the arm 103. By moving the arm 103 in a horizontal directionby a rotary shaft 104 having a motor, the near-field optical head 102can be scanned to an arbitrary point on the disk 101. The lightpropagated through an optical waveguide (or may be an optical fiber) 105connected to the arm 103 is introduced into an optical waveguide (lightintroducing part) provided inside the near-field optical head 102 forpropagating light in a direction parallel to the media surface, withoutimpeding a function of flexure (an optical fiber may be inserteddirectly in the head). The light passes through a reflection layer orfocusing function formed in the near-field optical head 102 andconverted by a very small aperture formed in a disk-side surface of thenear-field optical head 102 into near-field light, thus illuminated tothe disk 101. The scattering light caused by interaction of between thenear-field light and a microscopic area on the disk 101 surface isconverted into an electric signal by a light receiving element providedwithin the near-field optical head 102 or in the vicinity of thenear-field optical head 102 or on a back side of the disk 101 and fed toa signal processing circuit, thus reading-out microscopic areainformation. The near-field optical head 102 has a surface on a mediaside which may be formed in a flat plate surface to allow air damping orin a convex-and-concave form arranged and connected with severalparallelepiped plated (202, 302, 402) to provide an air stream passageas shown in FIG. 2 to FIG. 4. In the case of a planar surface, the verysmall aperture for producing near-field light will exist in the planarsurface. For a convex-and-concave surface, the very small aperture 203will exist in a plane on the media side of the joined parallelepipedplates 202 as shown in FIG. 2. Otherwise, as shown in FIG. 3 a conicalor pyramidal protrusion 304 may be formed between the parallelepipedplates 302 or on a surface in a lateral recessed area to form a verysmall aperture 303 at a tip thereof. Also, it is of course possible tohollow out the joined parallelepiped plate 402 and provide therein aconical or pyramidal protrusion 404 having a very small aperture 403formed at a tip thereof (FIG. 4).

Meanwhile, as a way to make the aperture and the media proximate indistance, a lubricant may be filled between the near-field light and themedia. By making constant the thickness of the lubricant due to rotationof the media or so and forming the near-field optical head sufficientlythin, the distance between the near-field optical head and the media canbe fully reduced by utilization of a surface tension of the lubricant.This enables to fully follow up deformation of the media and henceprovides effective means.

Here, explanation is made on the structure of the near-field opticalhead. FIG. 5 shows a sectional view of part of a near-field optical head500 according to Embodiment 1. In FIG. 5, on a silicon substrate 501having an aperture 506, an optical waveguide 504 is provided through alight reflection film 502 and further a light reflection film 503 isprovided thereon.

The silicon substrate 501 is forming a taper 507 in a manner penetratingthrough the same to have the very small aperture 506. The aperture 506has a microscopic diameter of less than 200 nano-meters so as to producenear-field light due to the light induced through the taper 507. Thetaper 507 is formed by forming the silicon substrate 501 with using ananisotropic silicon etching technology. On the taper 507 the lightreflection film 502 is formed to reflect the traveling light from theabove and collect an increased amount of light to the aperture 506.

The optical waveguide layer 504 is formed on the inner side of the taper507 and on the silicon 501. Also, on the optical waveguide layer 504 thelight reflection film 503 is formed in order to improve the reflectionefficiency of the mirror or the propagation efficiency through theoptical waveguide 504. The light outputted from a laser source orthrough the optical fiber, although not shown, is incident at a lightincident end 505 into the optical waveguide 504 and guided onto theaperture 506 by the optical waveguide 504. Above the aperture 506 amirror 508 is provided to change the direction of light. The lightpropagated via the optical waveguide 504 is reflected by the mirror 508and directed in traveling direction toward the aperture. The mirror 508is in a convex surface form to collect the reflection light to avicinity of the aperture 506.

Meanwhile, the mirror 508 may be formed with grating. Grooves are formedat nearly a pitch of a wavelength λ on the mirror 508. The lightreflected there is focused to the vicinity of the aperture 506 by virtueof the effect of grating. The light reflected by the mirror 508 andpropagating toward the aperture 506 is reflected by the light reflectionfilm 502 formed inside the taper 507, further being collected toward theaperture 506. The focusing as above provides collection of light withlocally high energy thus increasing the intensity of near-field light tobe caused at the aperture 506.

FIG. 6(A) and FIG. 6(B) are an explanatory view showing onemanufacturing process for a near field light head 500 shown in FIG. 5.FIG. 6(A) illustrates a shape as viewed from side while FIG. 6(B) ashape as viewed from top. First, in step S101 a taper 507 is formed in asilicon substrate 501 by an etching method having anisotropy forsilicon. For example, on a top surface of a silicon substrate having acrystal orientation (100), a thermal oxide film or nitride film isformed as a mask against anisotropic etching. An opening window isformed in the mask by using a photolithography technique usable in ausual semiconductor process to expose a silicon surface by etching.

Subsequently, the surface forming the opening window is exposed to anetch solution to form a four-surfaced taper of an inverted pyramidstructure in the silicon substrate 501. Then, the mask material formedon the silicon substrate 501 is removed thereby obtaining a siliconsubstrate 501 forming the taper 507. The etch solution uses, forexample, a potassium hydroxide (KOH) solution or tetramethylammoniumhydroxide (TMAH) solution that is different in etch rate depending upona planar orientation thereby easily enabling to form a taper. Also,alternative to immersion in an etch solution the taper can be formed byusing anisotropic etching, e.g. etching by an reactive ion etching (RIE)apparatus.

Subsequently, in step S102 the silicon substrate 501 is etched from thebackside to reduce the thickness of the substrate thereby forming a verysmall aperture 506 in the silicon substrate 501. Note that this etchingis ended at the formation of an aperture 506. As a result, an aperture506 is formed in a bottom of the taper 507. The aperture 506 is formedin a size of approximately 50 nm to 3 μm. The etching may use wetetching or dry etching.

Meanwhile, the aperture 506 may be formed in the process of step S101without performing the process of step S102. That is, the aperture 506can be formed by etching from the surface and through the siliconsubstrate 1.

Subsequently, in step S103 a material high in optical reflectivity, suchas aluminum (Al) or gold (Au), is laid inside the taper and on the topsurface of the silicon substrate to form a light reflection film 502.The formation of the light reflection film 502 makes it possible toreflect the propagation light in the vicinity of the aperture and focusit to the aperture 506. This result in intensification of the lightcollected to the aperture 506, thus producing intensified near-fieldlight.

Subsequently, in step S104 an optical waveguide 504 is laid over thelight reflection film 502. The material for the optical waveguide 504uses a dielectric material such as silicon oxide or silicon nitride, ora polymer material, such as polyimide or polymethacrylate. In the caseof silicon oxide, formation is easy by a sputter technique, a CVDtechnique or an evaporation technique. The optical waveguide 504 may beformed by core and clad that are different in reflectivity. In thiscase, propagation loss can be reduced because light propagates throughthe core while being totally reflected.

Meanwhile, in step S104 an optical waveguide 504 previously fabricatedmay be bonded to and formed on the light reflection film 502. In thiscase, the optical waveguide may be arranged only on the top surface ofthe silicon substrate 501 without forming the optical waveguide insidethe taper. The bonding method for the optical waveguide can use ananodic bonding technique, a metal bonding technique, and the like. Whereusing an anodic bonding technique, the light reflection film 502 on thesilicon substrate 501 is partly removed, and then silicon oxide as anoptical waveguide 504 is bonded to the silicon substrate surface. Whereusing a metal bonding technique, a material similar to the lightreflection film 502 is formed on a bonding surface of the opticalwaveguide 504 thereby bonded to the light reflection film 502.

Subsequently, in step S105 an optical waveguide 504 is controlled inshape using photolithography technique and etching. Using aphotolithography technique for use in usual semiconductor manufacturingprocesses, a mask material is laid and patterned on the opticalwaveguide 504 to protect against etching. Thereafter, the opticalwaveguide 504 is etched to remove the mask material, thereby patterningthe optical waveguide 504. A mirror 508 is simultaneously formed uponpatterning the optical waveguide 504.

The mirror 508 is formed to an angle so that the light traveling in ahorizontal direction can be reflected toward the aperture 506.Furthermore, a convex surface is provided to focus the reflected lightto a vicinity of the aperture 506. In order to form the mirror 508 insuch a form, the etching for the optical waveguide 504 uses dry etchingpossesses anisotropy as represented by reactive ion etching.

Also, the mirror 508 may be fabricated in a grating form. In this case,grooves are, made at a pitch of approximately a wavelength λ on themirror 508. The fabrication of grating can use a micro-fabricationtechnique, such as electron beam forming, dry etch method or focused ionbeam etching.

Finally, in step S106 a light reflection film 503 is formed on theoptical waveguide 504. The light reflection film 503 is formed by asputter technique or vacuum evaporation technique with using a highreflective metal material of Al or Au. Due to the light reflection film503, the mirror 508 reflects light and enables to collect an increasedamount of light to the vicinity of the aperture 506. This results inintensification of the light reaching the aperture 506 and hence makespossible to produce intensified near-field light. Furthermore, theprovision of the light reflection film 503 removes optical noises fromthe above or side.

As described above, the near-field optical head of Embodiment 1 of theinvention has a structure, in addition to the function of reflectinglight serving for focusing light, wherein an increased amount of lightcan be illuminated to the vicinity of the aperture. Accordingly,intensive near-field light can be easily produced.

Also, because the very small aperture can be formed by a technology usedin a semiconductor manufacturing process, a silicon substrate havingsuch an aperture facilitates particularly arraying having a plurality ofapertures formed on a same silicon substrate as a planar probe forproducing near-field light. Also because fabrication is through asilicon process, batch processing is made possible thus suited for massproduction. Also, fabrication can be a collective process on a wafer,there is less variation in the planar probes formed or the aperturesformed, thus stabilizing product property. Also, the probes can bereduced in size and the number of them per wafer be increased thusreducing cost.

Also, the near-field optical head according to Embodiment 1 is formed bythe usual semiconductor process. Accordingly, a plurality of them can beeasily arranged two-dimensionally on a common silicon substrate asdescribed above. FIG. 7 shows a structure of a near-field optical headarray 700 having near-field optical heads arranged in the form of atwo-dimensional array on a common silicon substrate. An opticalwaveguide 703 is formed such that the light illuminated from one lightsource 702 is guided to aperture top planes of four near-field opticalheads 701. The light illuminated by the light source 702 is illuminatedto an incident end of the optical waveguide 703 existing in an end faceof a silicon substrate 704 and then introduced into the opticalwaveguide 703. The introduced light passes through an inside of theoptical waveguide 703 and efficiently guided to vicinities of aperturesof the respective near-field optical heads 701 while being reflected bythe light reflection films provided in tapers similarly to FIG. 5. Due,to the guided light, near-field light is produced from each aperture. Inthe near-field optical head array 700 shown in FIG. 7 the fournear-field optical heads 701 on one silicon substrate 704 are arrangedfor the one light source. However, a variety of combinations arefeasible without limitation to this structure.

As described above, for the near-field optical head according toEmbodiment 1, a two-dimensional arrangement in plurality is structurallypossible on a common silicon substrate. Accordingly, head scanning isreduced to a minimum over a recording medium and optical recording andreading is possible at high speed. Furthermore, trackinglessness isrealizable by adapting the interval of arrangement to an interval ofinformation recording unit on the recording medium.

Embodiment 2

FIG. 8 shows a sectional view of a part of a near-field optical head 800according to Embodiment 2. In FIG. 8, an optical waveguide 804 isprovided through a light reflection film 802 on a silicon substrate 801having an aperture 806 and further a light reflection film 803 isprovided thereon, similarly to the near-field optical head 500 accordingto Embodiment 1. The aperture 806 has a microscopic diameter of lessthan 200 nano-meters in order to produce near-field light due to lightintroduced through a taper 807.

The near-field optical head 800 according to Embodiment is in astructure possessing a focusing function in the optical waveguide layer804 to cause light to be incident on a light incident end 805 for lightincidence. If as shown in FIG. 8 the light incident end 805 is made inshape in a convex surface form, the light emitted from a laser lightsource or optical fiber not shown in the figure is incident at the lightincident end 805 into the optical waveguide layer 804 and focused by alens effect of the light incident end 805. The focused light isreflected upon the mirror 808 toward a direction of the aperture 806 andilluminated to the vicinity of the aperture 806. The taper 807 in thevicinity of the aperture 806 is formed with a light reflection film 802in order to reflect the light transmitted through an upper portion, ofthe optical waveguide 804 and focus an increased amount of light to theaperture 806. The focusing in this manner collects locally high energyof light and increases the intensity of near-field light to be caused atthe aperture 806.

Meanwhile, the light incident end 805 can be made in a grating form. Insuch a case, grooves are formed at a pitch of approximately a wavelength% on the light incident end 805. Here, the light incident on the opticalwaveguide 804 is focused due to an effect of the grating and illuminatedto a vicinity of the aperture 806 by reflection upon the mirror 808.

The near-field optical head 800 of Embodiment 2 can be manufactured by amanufacturing process similar to the near-field optical head ofEmbodiment 1. The convex surface form in the light incident end 805 isfabricated by anisotropic etching in a process of step S105 shown inFIG. 6. For example, the form for a convex surface is formed usingreactive ion etching. Meanwhile, although a focusing function isprovided for the light incident end 805, it is needless to say that itmay be formed in the optical waveguide 804. Also, although in FIG. 8 thenear-field optical head shows an illumination mode as called in thenear-field optical microscope, it can also be utilized in a collectionmode.

As described above, the near-field optical head of Embodiment 2possesses a function of focusing light to a part of the opticalwaveguide, making possible to illuminate an increased amount of light toa vicinity of the aperture and hence easily produce intensive near-fieldlight in the vicinity of the aperture.

Also, because the very small aperture can be formed by the technologyfor use in the semiconductor manufacture process, the silicon substratehaving such an aperture can be utilized as a planar probe to producenear-field light. In particular, arraying is facilitated wherein aplurality of apertures are formed on a common silicon substrate. Becauseof fabrication through the silicon process, a batch process is feasiblethus being adapted for mass production. Also, a collective process on awafer reduces variation and stabilizes product characteristics. Becausethe probe can be reduced in size and the number thereof per waferincreases, cost can be lowered.

Embodiment 3

FIG. 9 shows a sectional view of part of a silicon substrateconstituting for a near-field optical head according to Embodiment 3. InFIG. 9, a silicon substrate is illustrated wherein a taper is formed bytwo different slant surfaces.

The near-field optical head of Embodiment 3 is improved in opticalefficiency in the vicinity of an aperture by making moderate the slantsurface in the vicinity of the aperture, i.e. widening the taper anglein the vicinity of the aperture. For propagation light in general,propagation loss is greater in a region where the optical waveguide forlight propagation is smaller in width than a wavelength λ. Accordingly,by widening the angle of the taper in the vicinity of the aperture, theregion that the width is smaller than the wavelength λ is decreased thusmaking possible to increase the amount of light reaching the aperture.This results in increase in intensity of near-field light to be causedthrough the aperture.

The taper 507 in the silicon substrate 501 shown in FIG. 5 wasfabricated using anisotropic etching on silicon thereby forming theslant surface on a (111) plane of the single crystal silicon. Due tothis, the angle defined between the taper 507 slant surface and thesilicon substrate 501 bottom surface is approximately 55 degrees.

Meanwhile, in the taper of the silicon substrate 901 shown in FIG. 9,the slant surface is formed by the two different crystal surfaces. Anupper-staged taper 902 has a comparatively abrupt gradient slant surfaceformed on a plane (111) of the silicon substrate, while a lower-stagedtaper 903 has a comparatively moderate gradient slant surface formed,for example, on a plane (311) of the silicon substrate. The aperture 904of the silicon substrate 901 thus structured has an angle ofapproximately 30 degrees given between the slant surface and the bottomsurface of the silicon substrate. Thus, a wider-angled form is providedas compared to the taper in the vicinity of the aperture formed in thesilicon substrate 501 shown in FIG. 5.

FIG. 10(A) and FIG. 10(B) are explanatory views showing one example of amanufacture process for the silicon substrate 901 shown in FIG. 9. FIG.10(A) illustrates a shape as viewed from the side while FIG. 10(B) ashape as viewed from the above.

First, in step S201 a mask material 905 is laid on a silicon substrate901 by using a photolithography technique for use in semiconductormanufacture, followed by being patterned. Note that the patterningshould be in a step-like form with two or more steps in shape. The maskmaterial 905 uses silicon oxide, silicon nitride, photoresist or thelike.

Subsequently, in step S202 an anisotropic etch technique of silicon isused to form a taper in the silicon substrate. In this etch technique,if etching is conducted for example with a potassium hydroxide (KOH)solution, a taper is easily formed because of a difference in etch ratedepending on a planar orientation of silicon.

Subsequently, in step S203 the mask material 905 is etched to form thetwo-staged mask material 905 into one-staged mask 906. Note that thisforming is possible by isotropically etching the mask material 905. As aresult, a top surface of the silicon substrate having a (100) planarorientation so far covered by the mask material 905 newly appear in amask opening window.

Subsequently, in step S204 anisotropic etching of silicon is conductedto form a taper with two stages in the silicon substrate 901. Where theetching is made by a KOH solution with different etch rate depending ona planar orientation, the slant surface for the upper taper 902 isformed on a plane (111) of the single crystal silicon whereas the slantsurface for the lower taper 903 is formed on a plane (311) of the singlecrystal silicon. Thus, the lower-staged taper 903 is in a slant surfacethat is moderate as compared to the upper-staged taper 902.

Subsequently, in step S205 the mask material 906 is removed away. Then,in step S206 the silicon substrate 901 is etched at a backside to reducethe thickness of the substrate thereby forming a very small aperture 904in the silicon substrate. Note that this etching should be terminated atformation of an aperture 904. As a result, an aperture 904 is formed ina bottom surface of the silicon substrate 901. The aperture 904 isformed to a size of approximately from 50 nm to 3 μm. The etching mayuse either wet etching or dry etching.

Using the silicon substrate 901 fabricated through the above steps, thesteps of S103 to S106 are carried out in order as was shown in FIG. 6 inEmbodiment 1. Thus, a near-field optical head is obtained which isprovided with an optical waveguide 504, a light reflection film 502, alight reflection film 503 and a mirror 508 in a concave surface form.Meanwhile, a light incident end 805 in a convex surface form can be alsoprovided similarly to that as was shown in Embodiment 2.

Incidentally, in the explanation of the near-field optical headaccording to Embodiment 3, FIG. 9 and FIG. 10 exemplified the taperforming the upper and lower two staged slant surfaces different inangle. Alternatively, a silicon substrate formed by a plurality of slantsurfaces, i.e. three or four stages, may be, used without limited to thetwo-staged slant surfaces.

As described above, the near-field optical head of Embodiment 3 of theinvention can be batch-processed and suited for mass production becauseof the fabrication through the silicon process as described above. Also,the capability of implementing the collective process on a wafer reducesvariation and stabilizes product characteristics. Also, size reductionis possible for the probe and the number thereof per wafer increasesthereby reducing cost.

Meanwhile, the structure with a very small aperture can be providedsimilarly to Embodiment 1 and utilized as a planar probe for producingnear-field light. Particularly, the structure having a plurality ofapertures on a common silicon substrate, i.e. arraying, is easy toimplement. Where used as an optical memory head, high-speed lightrecording and reading-out is feasible.

Also, in the near-field optical head according to Embodiment 3, becausethe silicon substrate 901 was used which is widened in taper form in thevicinity of the aperture 904 as shown in FIG. 9, the region having awavelength of or smaller is reduced in the optical waveguide at aposition in the vicinity of the aperture. Thus, the light propagationloss can be reduced in this region. As a result, the light focused tothe vicinity of the aperture can be efficiently converted intonear-field light.

Embodiment 4

FIG. 11 shows a sectional view of part of a silicon substrateconstituting for a near-field optical head according to Embodiment 4.This near-field optical head of Embodiment 4 is widened in taper anglein the vicinity of the aperture thereby reducing propagation loss in theregion where the optical waveguide for propagating light is smaller inwidth than the wavelength λ. Thus, the efficiency of light conversion isimproved for producing near-field light in the vicinity of the aperture.

In a silicon substrate 1101 shown in FIG. 11, a hole is formedpenetrating through the silicon substrate thus forming a very smallaperture 1103 in a bottom surface. A taper 1102 formed in the hole hasits slant surface given moderate in angle in the vicinity of theaperture 1103. The hole has, at an upper portion, a taper 1102 formed ata slant angle of approximately 55 degrees relative to the bottom surfaceof the silicon substrate 1101 and, in the vicinity of the aperture, ataper 1103 formed at a slant angle of approximately from 10 degrees to30 degrees.

FIG. 12 is an explanatory view showing one example of a manufacturingprocess for the silicon substrate 1101 shown in FIG. 11. First, in stepS301 a mask material 1104 is patterned over a silicon substrate 1101 byusing a photolithography technique for use in semiconductor manufacture,and then a taper is formed in the silicon substrate 1101 by using ananisotropic etch technique of silicon. For example, if etching isconducted by a potassium hydroxide (KOH) solution, the etch rate isdifferent depending on a planar orientation of silicon and hence a tapercan be formed with a slant angle of approximately 55 degrees.

Subsequently, in step S302 isotropic etching of silicon is conducted.For example, the etching by XeF₂ isotropically etches the silicon. Theisotropic etching turns a bottom of the taper 1102 from a sharp forminto a round form. As a result, the slant surface of the taper 1102 inthe vicinity of the bottom will be from 10 degrees to 30 degreesrelative to the bottom surface of the silicon substrate 1101.

Subsequently, in step S303 the mask material 1104 is removed away.Subsequently, in step S304 the silicon substrate 1101 is etched at itsbackside to reduce the thickness of the substrate thereby forming a verysmall aperture 1103 in the silicon substrate. Note that this etching isterminated at the formation of an aperture 1103. As a result, anaperture 1103 is formed in the bottom surface of the silicon substrate1101. The aperture 1103 is formed to a size of from 50 nm to 3 μm.Meanwhile, FIG. 13 is an explanatory view showing another example of amanufacturing process for the silicon substrate 1101 shown in FIG. 11.

In FIG. 13, first in step S401 a mask material 1304 is patterned over asilicon substrate 1301 by using a photolithography technique for use insemiconductor manufacture similarly to the step S301 of FIG. 12, andthen a taper is formed in the silicon substrate by using an anisotropicetching technique for silicon. The mask material 1304 in this case usesa silicon oxide film.

Subsequently, in step S402 a silicon oxide film 1305 is formed over theperiphery of the silicon substrate 1301. The silicon oxide film 1305 ismade by putting the silicon substrate 1301 in a hot thermal oxidationoven to cause oxidation on the surface of the silicon substrate 1301.The oxidation film tends to be less formed in the bottom of the taper.As a result, the silicon oxidation film 1305 at the taper bottom issmaller in thickness as compared to the thickness of the silicon oxidefilm 1305 at a taper slant surface.

Subsequently, in step S403 is removed the silicon oxide film 1305 formedon a periphery of the silicon substrate 1301. The thickness of thesilicon oxide film 1305 in a taper bottom is smaller than the thicknessof the silicon oxide film 1305 on the taper slant surface, consequently,the taper 1302 of the silicon substrate 1301 after removal of thesilicon oxide film 1305 has a shape becoming moderate in slant surfaceangle and round as the bottom is approached. As a result, the slantsurface at the bottom of the taper 1302 has an angle of from 10 degreesto 30 degrees relative to the bottom surface of the silicon substrate1301.

Subsequently, in step S404 the silicon substrate 1301 is etched at abackside similarly to the step S304 of FIG. 12 to form a very smallaperture 1303 of approximately from 50 nm to μm in the silicon substrate1301. In the manufacturing process for the near-field optical headaccording to Embodiment 4, the steps S103 to S106 of Embodiment 1 arecarried out in order by using a silicon substrate 1301 fabricatedthrough the processes as above or a silicon substrate 1101.

As described above, the near-field optical head of Embodiment 4 of theinvention can be batch-processed and suited for mass production becauseof the fabrication through the silicon process as described above. Also,the structure with a very small aperture can be provided similarly toEmbodiment 1 and utilized as a planar probe for producing near-fieldlight. Particularly, the structure having a plurality of apertures on acommon silicon substrate, i.e. arraying, is easy to implement. Whereused as an optical memory head, high-speed light recording andreading-out is feasible.

Also, in the near-field optical head according to Embodiment 4, becausethe silicon substrate 1101 was used which is widened in taper form inthe vicinity of the aperture 1103 as shown in FIG. 11, the region havinga wavelength of λ or smaller is reduced in the optical waveguide at aposition in the vicinity of the aperture. Thus, the light propagationloss can be reduced in this region. As a result, the light focused tothe vicinity of the aperture can be efficiently converted intonear-field light.

It should be noted that the near-field optical head according toEmbodiment 1-4 can be used as an optical probe for optical microscopesbesides as a near-field optical head as an optical memory head.

Embodiment 5

Next, explanations will be made on a method of forming with accuracy andreproducibility the aperture thereof into a targeted size or shape in aplanar probe as a near-field optical head according to Embodiment 1-4explained above.

Usually, in a planar probe a light reflection film as explained inEmbodiment 1 is formed on the taper in order to guide propagation lightefficiently to the very small aperture. The light reflection film isprovided to reflect thereon propagation light to be introduced to theaperture of the near-field optical head. The size and form of anaperture has been defined by an edge of a hole formed due toimplementing an etch process as was shown in FIG. 6.

Accordingly, the thickness of the light reflection film has beenselected in such a degree that has no effect upon the hole edge in thesilicon substrate. However, as discussed in the “Problem that theInvention is to Solve”, where a very small aperture is formed by an etchprocess, variations in the size and shape will frequently occur. Even ifaccurate control can be implemented in forming a light reflection filmto a small thickness, it has been impossible to obtain intensivenear-field light intended as a planar probe.

The manufacturing method for a near-field optical head according toEmbodiment 5 is to form an aperture having a size greater than a targetsize or different in shape from a targeted shape by an etch process orthe like on a silicon substrate and form an increased thickness of alight reflection film on a taper thereby defining a final size or shapeof the very small aperture.

FIG. 14 is a sectional view of an aperture formed in a silicon substrateby a method of anisotropic etching, isotropic etching or the like. InFIG. 14, a very small aperture 1403 is provided by forming a taper 1402in a silicon substrate 1401. However, this very small aperture 1403 isgreater than a targeted size or in a shape different in shape from atargeted shape.

A light reflection film is formed on a surface of the silicon substrate1401. The formation of such a light reflection film is usuallyimplemented by using a sputter technique, a CVD method, an evaporationtechnique or the like, and achieved by gradually depositing (hereunder,referred to as film-forming) a particle matter of a material, such asaluminum (Al) or gold (Au), having a high reflectivity for a wavelengthλ of propagation light used for producing near-field light on an object(in this case, particularly on the taper 1402).

In FIG. 14, the arrow A and the arrow B represents a direction of filmforming, i.e. an arriving direction of the particles mentioned above.Usually, film formation is in a vertical direction with respect to asilicon substrate 1401 as shown at the arrow A. It is however possibleto form a film by shifting the film-forming angle, for example, as shownat the arrow B.

FIG. 15 is a sectional view of an aperture formed in the siliconsubstrate after film formation. In FIG. 15, a metal film 1504 isfilm-formed as a light reflection film in a film thickness of t. Here,the film thickness represents a thickness of the metal film 1504 from atop surface of the silicon substrate 1401 in a vertical direction to thetop surface of the silicon substrate 1401 (the surface except for thetaper 1402). By film-forming a metal film 1504 to a sufficient thicknesson the taper 1402, in a periphery of the very small aperture 1403 themetal film 1504 protrudes by a protrusion amount Δr toward a center ofthe very small aperture 1403 to form a very small aperture having a sizeD (hereafter, referred to as a very small aperture after correction)smaller than a size d of a former very small aperture (hereafter,referred to as a very small aperture before correction). That is, theintensity of near-field light to be produced is defined by the verysmall aperture after correction. Accordingly, a relationship D=d−2Δrstands. Here, the protrusion amount Δr denotes a length of from an edgeof the very small aperture before correction to a protrusion of themetal film 1504 in a direction along a bottom surface of the siliconsubstrate 1401.

Also, as shown in FIG. 15 the size D of the very small aperture aftercorrection is defined not by the metal film 1504 in a direction along abottom surface of the silicon substrate 1401 but in a position deviatedabove by Δz from the bottom surface of the silicon substrate 1401. Thatis, this Δz represents a deviation in height between the aperture aftercorrection and the aperture before correction. Here, it is satisfactoryto meet a condition for producing near-field light if given D<λ.However, there is a need to satisfy a relationship of D<λ/2 because ofnecessity of an aperture size smaller than a diffraction limit.

Because the protrusion amount Δr is proportional to a film thickness t,the size D of a very small aperture after correction can be controlledby the thickness t. FIG. 16( a) is a top view of a very small aperture,after correction where the direction of film forming is taken at thearrow A in FIG. 14. As shown in FIG. 16( a), an aperture formed deviatedinward by a protrusion amount Δr from the very small aperture beforecorrection 1403 provides a size and shape effective for producingnear-field light:

FIG. 17 is a figure showing a relationship of a film thickness t and aprotrusion amount Δr where Al is film-formed in the film formingdirection A onto the taper. Particularly, FIG. 17 shows respectivegraphs for cases implementing as a film-forming method a vacuumevaporation method and a sputtering method. Incidentally, thefilm-forming condition in this case is taken a vacuum degree of 3×10⁻⁶torr and an evaporation rate of 700 angstroms/min. for the vacuumevaporation method. The grain size in evaporation is comparatively smallto provide homogeneous film formation on the taper. Also, the sputtermethod uses a vacuum degree of 3×10⁻³ torr and an evaporation rate of200 angstroms/min. The grain size is comparatively small and the filmthickness decreases as the bottom of the taper is neared. Consequently,the protrusion amount is smaller than the case with the vacuumevaporation method.

From FIG. 17 the relationship between a film thickness t and aprotrusion amount Δr is representable as Δr>t/10. That is, under theabove film forming condition the protrusion amount Δr will not beone-tenth of a film thickness t or less. In a case that the protrusionamount Δr be assumingly in a relation of one-tenth of a film thickness tor less, a very thick film must be formed in order to control the sizeand shape of an aperture resulting in inefficiency. It is thereforepreferred to forming a film nearly under the above film formingcondition. Meanwhile, in the vacuum evaporation method the protrusionamount Δr can be increased to nearly Δr=t/2 by decreasing theevaporation late slower than the above film forming condition andincreasing the grain size.

FIG. 18 is a figure showing a relationship between a film thickness tand a height deviation Δz of a maximum protrusion from a bottom surface.In particular, FIG. 18 illustrates a graph for a case of implementing avacuum evaporation method as a film forming method, wherein the filmforming condition is as per the above. It is possible from FIG. 18 toexpress as Δz˜t/3. That is, as the film thickness t increases, theheight deviation Δz also increases.

From FIG. 17 and FIG. 18, where the film thickness t is increased toincrease the protrusion amount Δr, the size D of a very small apertureafter correction decreases but the height deviation Δz also increaseswith a result that the aperture position effective for producingnear-field light will be distant from the bottom surface. This meansthat the intensity of near-field light decreases with increase in heightdeviation Δz, from a nature that near-field light exponentiallyattenuates as being distant from the aperture. Also at the same time,because near-field light spreads as being distant from the very smallaperture, the reduction in resolving power is meant. For example, if thevery small aperture and a recording medium is distant to nearly a sizeof the very small aperture, the resolving power is halved. Provided thatthis distance is a limit of resolving power, the size D of a very smallaperture after correction can be expressed Δz<D=d−2Δr. Therefore, Δz isnot preferred to increase but desirably held as small as possible.

Meanwhile, in the vacuum evaporation method, the very small apertureafter correction can be controlled in shape for example by tilting thefilm forming direction. FIG. 16 (b) is a top view of a very smallaperture after correction where the film forming direction is taken atthe arrow B in FIG. 14. FIG. 16( b) shows a case that the arrow B is ina direction tilted by 20 degrees relative to a direction vertical to thesilicon substrate 1401. As shown in FIG. 16( b), the metal film isformed thick on a surface facing the direction of evaporation. The metalfilm is formed thin on an opposite-side surface. It was confirmed thatthe increase/decrease amount of the protrusion amount was approximately20% of the protrusion amount Δr for the case of FIG. 16( a).

As an exemplification, in the case of film forming by a vacuumevaporation method, if a film thickness of Al is taken t=150nano-meters, then Δz=40-50 nano-meters and Δr=70-80 nano-meters whereinthe size (diameter) of a very small aperture before correction is d=250nano-meters, whereas the size of a very small aperture after correctionis D=100 nano-meters. This satisfies the above formula Δz<D. In the caseof film forming by a sputter method, height deviation Δz and protrusionamount Δr are smaller than those in the vacuum evaporation method, whichnaturally satisfies Δz<D.

In the above, explanation was made for the case of forming a film on thetaper 52. Alternatively, it is also possible to form a film on abackside of a silicon substrate 1401 and control the size and shape of avery small aperture. FIG. 19 is a sectional view of an aperture formedafter forming a film on a silicon substrate backside. Note that, in thefigure, the lengths common in meaning to those of FIG. 15 are denoted atthe same reference numerals to omit explanations thereof.

In FIG. 19, where implementing a vacuum evaporation method as a filmforming method, when the film is formed on the taper 1402 there isalmost no difference in the relationship between a film thickness t anda protrusion amount Δr. However, where implementing a sputter method,the relationship between a film thickness t and a protrusion amount Δris that the protrusion amount Δr with respect to the thickness tincreases because an obstacle such as the taper 1402 does not exist.

Meanwhile, the relationship between a film thickness t and a heightdeviation Δz is similar to the graph shown in FIG. 18 or in a tendencyof further decrease in the height deviation Δz. However, in this case,the height deviation Δz differs from a case of forming a film on thetaper 1402 because, as it increases, the aperture effective forproducing near-field light is provided closer to a recording medium.Accordingly, in FIG. 19 the size of a very small aperture aftercorrection D can be expressed as t−Δz<D=d−2Δr. Due to this, the filmthickness t cannot be increased.

Also, where film forming is made on both the taper 1402 and the siliconsubstrate backside, basically the very small aperture effective forproducing near-field light is defined by a smallest area. In such acase, near-field light can be efficiently produced by decreasing thedistance between a smallest aperture and a bottom surface of a planarprobe.

It should be noted that the film thickness t explained above may begreater than a light intrusion length (propagation light infiltrationwith respect to the metal film) wherein even if less than the intrusionlength no especial problem occurs except for mere decrease inreflectivity. The protrusion amount Δr and protrusion shape differdepending on the method and condition of film forming. In the case ofevaporation, the protrusion amount is decreased because of welldirectionality. In the film forming inside the taper, however, the filmis sufficiently formed even to the vicinity of the aperture. Meanwhile,in the sputter method the protrusion amount increases because of muchoccurrence of deep arrival. However, in film forming on the taper thereis a tendency of less film forming in the vicinity of the aperture.

Also, the silicon substrate may be thin in a case of using SOI (siliconon insulator) or thick, e.g. approximately 500, as in a usual case. Thetaper form and manufacture method are not only by anisotropic etchingbut may be by isotropic etching to provide an arcuate form, thus notbeing especially limited. Also, a glass substrate can be employedinstead of the silicon substrate, to form a taper by isotropic etchingor the like.

In the above near-field optical head manufacturing method in Embodiment5 of the invention, an aperture greater than a targeted size or shape isformed in a silicon substrate, and a light reflection film to be formedon a taper of the aperture and/or a silicon substrate backside iscontrolled in amount, thereby defining a size and shape of a very smallaperture for producing near-field light. Accordingly, it is possible tosolve the problem with deviation caused upon microscopically forming anaperture in the silicon substrate by an etch process or the like, by afilm forming process comparatively easy to control. Thus, a planar probecan be obtained with yield.

Embodiment 6

Next, explanations will be made on another manufacturing method for anear-field optical head having a very small aperture controlled in sizeor shape. As was shown in Embodiment 5, a very small aperture is formedin a silicon substrate, followed by thermal oxidation. At this time, athermal oxidation film being formed on a surface can be controlled infilm thickness depending on a degree of oxidation. However, becausevolumetric change is occurring in the area being oxidized, the amount ofthis volumetric change also can be controlled. FIG. 20 is a sectionalview illustrating a manner that volumetric change is caused and the verysmall aperture changes in size. As shown in FIG. 20, the formation of athermal oxidation film 2005 changes the shape of a former taper and verysmall aperture (wave lines in the figure) into a shape shown by solidlines.

The oxidation of a silicon substrate (usually thermal oxidation) causesvolumetric change depending upon a oxidation film thickness (usuallyapproximately 1.2 microns at maximum). Although the former shape isshown by dotted lines, the volumetric change provides a solid-linedform. An oxidation film region is formed outward and inward inapproximately 1:1. Because the thermal oxidation film thickness in usualis approximately 1.2 microns at maximum, the aperture can be madesmaller by inwardly 600 nano-meters at maximum (approximately 1.2microns in diameter). After ion implant or so, there is a possibilitythat the film thickness be further increases.

Controlling the oxidation film thickness enables control of volumetricchange, i.e. protrusion amount. Note that, because the oxidation film istransmissive of usual light (visible light, etc.), usually a metal filmis necessary in forming a very small aperture. However, such a metalfilm is satisfactory if can provide shading, and may not be so thick aswas shown in Embodiment 5. The metal film may be either on an upper sideor on a lower side, wherein merely changed is the emission efficiency oflight through the very small aperture. Besides thermal oxidation, ionimplanting can be utilized because ion implant changes silicon amorphousand causes volumetric change. With other methods of causing volumetricchange, there is no limitation to thermal oxidation and ion implant.

In the above near-field optical head manufacturing method in Embodiment6 of the invention, an aperture greater than a targeted size or shape isformed in a silicon substrate, and thermal oxidation or ion implant ismade on or to a surface including a taper of the aperture, therebydefining a size and shape of a very small aperture for producingnear-field light. Accordingly, it is possible to solve the problem withdeviation caused upon microscopically forming an aperture in the siliconsubstrate by an etch process or the like, by a thermal oxidation or ionimplant process comparatively easy to control. Thus, a planar probe canbe obtained with yield.

Embodiment 7

FIG. 21 shows a sectional view of a part of a near-field optical head2100 according to Embodiment 7. The near-field optical head 2100according to the present embodiment is structured by a planar substrate2101 having a hole in an inverted pyramid form having an apex forming avery small aperture, an optical propagation member in the form of anoptical waveguide 2103 for propagating light to the very small aperture,a protrusion 2102 structured by a part of the optical waveguide 2103 andhaving a pyramid form protruding from the very small aperture, and alight reflection layer 2104 formed on a periphery of the opticalwaveguide 2103 in an area except for the protrusion 2102 to reflect thelight propagating through an inside of the optical waveguide 2103. Asillustrated, the optical waveguide 2103 extends continuously from thelight incident end 2105, through the very small aperture and terminatesin the protrusion 2102. The optical waveguide 2103 may be structured bya core for propagating light and a clad provided on an outer peripherythereof. The clad has a reflectivity relatively low as compared to areflectivity of the core.

Although not shown in FIG. 21 the light outputted from a laser lightsource or through an optical fiber is incident on a light incident end(side) 2105 to the optical waveguide 2103, and propagates toward a tipof the optical waveguide 2103, and propagates toward a tip of theoptical waveguide 2103 while being reflected by the light reflectionlayer 2104 formed on a periphery of the optical waveguide 2103. Owing tothe reflection effect by the light reflection layer 2104, an increasedamount of light can be supplied to the tip of the optical waveguide2103. The planar substrate 2101 is formed with an optically very smallaperture. The optical waveguide 2103 at its tip protrudes from the verysmall aperture and forms a protrusion 2102 in a pyramid form. Theprotrusion 2102 has a size having a height of less than 200 nm and abottom-surface side length of less than 200 nm, wherein the lightreflection layer 2104 is not formed thereon. This protrusion 2102because of structured by one part of the optical waveguide 2103propagates an increased amount of light to the protrusion 2102. As aresult, an increased amount of near-field light converted from thepropagation light can be produced in a periphery of the protrusion 2102protruding from the very small aperture. Also, the tip (protrusion 2102)of the pyramid-formed optical waveguide 2103 protruding from the planarsubstrate 2101 has a ratio of height and bottom-surface one side ofapproximately √3−2:2, and is structured that a region the opticalwaveguide in width is smaller than a wavelength of light is very short.As a result, the attenuation of light intensity is reduced in the regionthe optical wavelength width is smaller than a light wavelength thusenabling supply of intensive near-field light through the protrusion2102. By thus arrange in proximity the protrusion 2 where the greaterpart of near-field light is localized to a sample surface, near-fieldlight can be scattered at a sample surface to derive optical informationon a very small area of light (illumination mode).

Otherwise, the near-field light localized at a sample surface isscattered by the protrusion 2102 at the tip of the optical waveguide2103 and derived as propagation light and then introduced at a rear of alight introducing end 2105 to a detector. This can also detect opticalinformation on a very small area collection mode). In also this case,because the region that the optical waveguide width in the protrusion2102 at the tip of the optical waveguide 2103 is smaller than a lightwavelength of light is structured fully narrow, the greater part ofnear-field light can be scattered into propagation light and be guidedwith reduced propagation loss to the light introducing end by the lightreflection layer 2104.

Meanwhile, where near-field light is produced at the very small apertureprovided on the planar substrate as in a planar probe discussed in theconventional art, the resolution (resolving power) of an obtainableoptical image is nearly in a same degree as the size of the aperture.However, in the near-field optical head 2100 shown in FIG. 21,near-field light is localized at around the protrusion 2102 as a part ofthe optical waveguide protruding from the very small aperture, which hasa resolving power corresponding to a radius of curvature of theprotrusion tip. Accordingly, it is possible to detect an optical imagewith resolution (resolving power) from the optical image obtainedthrough the very small aperture.

Also, in the near-field optical head 2100 shown in FIG. 21, although thelight reflection film 2104 is not formed on a periphery of theprotrusion 2102 protruding from the very small aperture, lightreflection film 2104 may be structurally provided on a periphery of theprotrusion 2102 and an optical aperture be formed at a tip of theprotrusion 2102. In this case, an increased amount of light can besupplied to a vicinity of the protrusion 2102 tip by the effect of thelight reflection film 2104 formed on a periphery of the protrusion 2102.

FIG. 22 is an explanatory view showing a manufacture process for thenear-field optical head shown in FIG. 21.

First, in step S501 a substrate uses a silicon substrate 2200 that is asingle crystal silicon having a (100) planar orientation. It is alsopossible to use a single crystal silicon with a planar orientation of(110) or (111), a dielectric crystal such as of glass and quartz, or asemiconductor crystal such as GaAs.

Next, in step S502 a recess 2201 in an inverted pyramid form is formedin the silicon substrate 2200 by an etch method with anisotropy forsilicon. A thermal oxidation film as a mask material is formed on thesubstrate and patterned in desired areas by photolithography and etchingthus exposing the silicon. Etching is made on the silicon in patternedareas by crystal-axis anisotropic etching with a potassium hydroxidesolution or tetramethylammonium hydroxide solution. At this time, arecess 2201 in an inverted pyramid form is formed surrounded by foursurfaces equivalent to the plane (111). Also, alternative to immersionin an etch solution, the recess 2201 can be formed by using anisotropicdry etching, e.g. by a reactive ion etching (RIE) apparatus. The maskmaterial may use SiO₂ or a nitride film in place of the thermal oxidefilm. Thereafter, the thermal oxide film as a mask material is removedaway by a mixture solution of hydrofluoric acid and ammonium fluoride.

Next, in step S503 a light reflection layer 2202 is formed. Film formingis made by a vacuum evaporation method such that a reflective metal filmof Au, Al or the like is buried to a bottom of the recess 2201. Thecovering method may use a sputtering method or ion plating method. Theprovision of a light reflection film 2202 makes it possible to guide tothe aperture the light propagating through the optical waveguide, alsoserving as a shade film against external light.

Next, in step S504 an dielectric as an optical waveguide 2203 isfilm-formed over a top surface of the light reflection film 2202. Thematerial for the optical waveguide 2203 may use a dielectric materialsuch as silicon oxide or silicon nitride or a polymer material such aspolyimide or polymethacrylate. In the case of silicon oxide as adielectric material, formation is easy by a sputter technique, a CVDtechnique or a vacuum evaporation technique. The optical waveguide 2203may be formed by a core and a clad that are different in reflectivity.In this case, light propagates by total reflection through the core,thus reduced in propagation loss.

Next, in step S505 the substrate is etched at a backside to form in thesubstrate a microscopic protrusion 2204 in a pyramid form covered by alight reflection film 2202. The substrate is reduced in thickness byetching the silicon substrate 2200 at its backside. The etching isterminated at the formation of a pyramid-formed microscopic protrusion2204 of the light reflection film 2202. The pyramid is formed to a sizeof one side of approximately 50 nm to 3 μm. The etching on the siliconsubstrate 2200 may use wet etching or dry etching.

Next, in step S506 the metal film as the light reflection film 2202 isetched from the backside of the substrate to form a very small aperturehaving a size of one side of 50-200 nm. Simultaneously, a protrusion2205 is formed as a part of the optical waveguide removed of the lightreflection film. The etch amount of the metal film is controlled toadjust for a size of the aperture in the metal film. This result information of a pyramid-formed microscopic protrusion 2205 of adielectric material positioned at a tip of the optical waveguide 2203.Upon AFM operation, this protrusion 2205 at its apex serves a role of aprobe. The etching on the metal film may use dry etching or wet etching.

Next, in step S507 the optical waveguide 2203 is made to a form by usinga photolithography technology and etching. Using a photolithographytechnology for use in the usual semiconductor process, a mask materialfor protection against etching is laid on the optical waveguide 2203 andthe mask material is patterned. Thereafter, the optical waveguide 2203is etched and the mask material is removed away. Thus, the opticalwaveguide 2203 can be patterned. In order to reduce the roughness at anend surface of the optical waveguide 2203, the etching on the maskmaterial and optical waveguide material uses anisotropic dry etching asrepresented by reactive ion etching or induction plasma etching. Themask material uses amorphous silicon, polysilicon, a metal film such asof Cr, Al, WSi, Ni and Au, or photoresist.

Next, in step S508 a light reflection film 2206 is film-formed on a topsurface of the optical waveguide 2203. A metal film, such as of Au orAl, high in reflectivity is formed by a vacuum evaporation technique.The covering method may use film forming using a sputter technique orion plating technique. The provision of a light reflection film 2206makes it possible to focus to the aperture the light propagating throughan inside of the optical waveguide 2203, also serving as a shade filmagainst external light.

The near-field optical head 2100 shown in FIG. 21 can be fabricated bythe procedure as shown above. However, the near-field optical head 2100shown in FIG. 21 can be fabricated similarly if the processes of stepsS507 and S508 are performed before the processes of steps S505 and S506.

As described above, the near-field optical head 2100 of Embodiment 7 ofthe invention is structured having a function of reflecting light. Also,in the vicinity of the aperture of the light reflection film 2104positioned at a tip of the optical waveguide, the region the opticalwaveguide width is smaller than a light wavelength is in a narrowstructure to reduce light loss at around the protrusion 2102. Theprotrusion 2102 not covered by the light reflection film 2104 can easilyproduce intensified near-field light. Also, it is possible to conductoptical image measurement or surface shape observation with resolutionequivalent to a radius of curvature at the tip of the protrusion 2102.

Meanwhile, because the very small aperture and the protrusion forproducing near-field light can be easily formed by the technology foruse in the semiconductor manufacture process, arraying is facilitated toform a plurality of near-field optical heads on a common siliconsubstrate. Also, because of manufacture through the silicon process,batch process is possible to implement thus suited for mass production.Also, because of manufacture by the collective process on the siliconwafer, variation is reduced. Furthermore, product characteristics arestabilized. Also, the probe can be reduced in size and accordingly thenumber per wafer increases, thus reducing cost.

In the case that a material to which a phase change recording medium isapplicable is used for a material of a recording medium, the increase ofoptical density is an important factor because recording thereof uses anoptical energy heat mode. Accordingly, for optical memory utilizingnear-field light, there is a desire of producing a sufficiently highintensity of near-field light. In the optical memory head of theinvention, the increase in intensity of near-field light is achieved bythe focusing action of the light reflection layer shown in FIG. 21 to adirection toward the aperture or the reduction in width of the opticalwaveguide to a wavelength or smaller by the pyramid form at the tip ofthe optical waveguide. Also, data reading and writing are possible at abit interval corresponding to a tip diameter of the microscopicprotrusion shown in FIG. 21, thereby realizing the density increase ofoptical memory storage bit. The above explanations are on anillumination mode in so-called a near-field optical microscope whereinnear-field light is produced by focusing light to a protrusion of anoptical memory head. However, the near-field optical head according tothe invention is effective in so-called a collection mode wherein lightis illuminated by another optical system to a recording medium surfaceso that a microscopic protrusion detects near-field light produced by amicroscopic information recording structure on the recording mediumsurface. In such a case, the near-field light detected by the protrusionis converted into scattering light and propagates through the opticalwaveguide reaching the light incident end. Accordingly, a photodetectoris arranged close to the light incident end.

Also, the near-field optical head for use as an optical memory headaccording to Embodiment 7 is formed by the usual semiconductor processand hence can be easily two-dimensionally arranged in plurality on acommon silicon substrate.

FIG. 23 shows a structure of near-field optical head array 2300two-dimensionally arrayed with the optical memory heads on a commonsilicon substrate. An optical waveguide 2303 is formed such that thelight illuminated from one light source 2302 is guided to protrusion topsurfaces of four near-field optical heads 2301. The light illuminated bythe light source 2302 is illuminated to an incident end of the opticalwaveguide 2303 existing at an end face of the silicon substrate 2304 andincident to the optical waveguide 2303. The incident light passesthrough the optical waveguide 2303 and efficiently guided to vicinitiesof protrusions of the optical memory heads 2301 while being reflected bylight reflection films provided in tapers similarly to FIG. 21. By theguided light, near-field light is produced at each protrusion. In thenear-field optical head array 2300 shown in FIG. 23, for one lightsource the four near-field optical heads 2301 are described on onesilicon substrate 2304. However, the invention is not limited to thisbut various combinations are possible to implement.

As described above, because the near-field optical heads for use as anoptical head according to Embodiment 7 can be two-dimensionally arrangedin plurality on a common silicon substrate, the head scanning is reducedto a minimum over a recording medium. Thus, high-speed optical storingand reading is possible. Furthermore, trackinglessness can be realizedby adapting the interval of arrangement to an information recording unitinterval on the recording medium.

Embodiment 8

FIG. 24 shows a sectional view of a part of a near-field optical head2400 according to Embodiment 8.

In FIG. 24, the near-field optical head 2400 according to Embodiment 8is structured, similarly to the near-field optical head 2100 accordingto Embodiment 7, by a planar substrate 2401 having a very smallaperture, a pyramid-formed protrusion 2402 protruding from the verysmall aperture to detect and illuminate near-field light, an opticalwaveguide 2403 for propagating light to the protrusion, and a lightreflection layer 2404 formed on a periphery of the optical waveguide toreflect the light propagating through the optical waveguide.

In the near-field optical head 2400 according to Embodiment 8, as shownin FIG. 24 a hole is formed in the planar substrate 2401 which is formedby two-staged slant surfaces different in angle. The slant surface closeto an entrance of the hole is in a broader form. Consequently, theoptical waveguide 2403 formed on the slant surfaces is bent in form attwo points. In this case, the propagation light will have a refractionangle reduced at one bent point of the optical waveguide 2403 wherelight propagation loss is decreased. As a result, the light propagationloss is totally reduced at the two bent points formed in the opticalwaveguide 2403, thus enabling to illuminate an increased amount of lightonto a sample.

Incidentally, FIG. 24 showed the planar substrate having the holestructured by two stages of slant surfaces different in angle.Alternatively, it is of course possible to use a planar substrate havinga hole structured by three stages, four stages or a multiplicity ofstages of slant surfaces without limited to two stages.

The near-field optical head of Embodiment 8 can be manufactured by aprocess similar to the fabricating method for the near-field opticalhead of Embodiment 7. Using a silicon substrate 2200 structured havingan inverted pyramid recess in the substrate shown in step S501, in stepS512 a thermal oxidation film as a mask material is again formed on thesubstrate. Patterning is made in desired positions by photolithographyand etching to expose silicon, thereby etching the silicon in thepatterning. In this case, in S111 silicon is exposed and etched over abroader range including the etched points. As a result, a surface occursthat is different in planar orientation from a tangential line of a(100) plane and a (111) plane of the silicon substrate. Thus, a siliconsubstrate is prepared which has a recess 2207 having two stages of slantsurfaces different in angle shown in step S512.

Thereafter, the processes of from step S503 to step S508 are carried outsimilarly to the near-field optical head of Embodiment 7 shown in FIG.22, thereby manufacturing a near-field optical head 2400 of Embodiment 8shown in FIG. 24.

As described above, in the near-field optical head of Embodiment 8 ofthe invention, the optical waveguide is bent in multiple stages toreduce the refraction angle of propagation light at one bent pointthereby totally reducing light propagation loss at the bent points,making possible to illuminate an increased amount of light to theprotrusion for producing near-field light and hence easily produceintensified near-field light. Also, an optical image can be obtainedwith resolution equivalent to a tip diameter of the protrusion.

Meanwhile, similarly to Embodiment 7, because the very small apertureand the protrusion can be formed by the technology for use in thesemiconductor manufacturing process, the silicon substrate having such aprotrusion can be utilized as a planar probe for producing near-fieldlight and compact in structure, particularly facilitating arraying toform a plurality of protrusions on a common substrate. Also, themanufacture through the silicon process enables batch processing thussuited for mass production. Also, the manufacture with collectiveprocesses on the wafer reduces variation and further stabilizes producecharacteristics. Also, the probe can be reduced in size and the numberper wafer increases hence reducing cost.

As described above, the near-field optical head according to Embodiment7 and Embodiment 8 are usable as a near-field optical head for opticalmicroscopes besides as a near-field optical head for recording andreading-out apparatuses. It is also possible, using the protrusion tip,to observe a surface shape or form a microscopic structure withutilizing an interaction such as of tunneling current or interatomicforce. Otherwise, a magnetic film may be put on the tip to observe amagnetic field on a surface of a sample.

Embodiment 9

Hereunder, embodiments of the invention will be explained with referenceto the drawings. FIG. 25 is a side sectional view showing a structure ofa near-field optical head 2500 according to Embodiment 9 of theinvention. In the near-field optical head 2500 shown in FIG. 25, anoptical waveguide 2501 is structured by a clad 2502, a core 2503 and aclad 2504, wherein the laser light La emitted from a laser light source(not shown) is propagated with low loss.

Also, the optical waveguide 2501 is formed of a dielectric material suchas a quartz-based material or polymer, and structured by the clad 2502,the core 2503 and the clad 2504. Here, the optical waveguide 2501 isstructured such that the core 2503 has a reflectivity greater than areflectivity of the clad 2502 and clad 2504. The clad 2502 is formed bydepositing a silicon dioxide film through a technique such as CVD(Chemical Vapor Deposition), sputtering or evaporation. At one endthereof, an inverted cone-formed taper hole 2502 a is formed which isgradually reduced in diameter in a taper form in a direction from asurface toward a backside. This taper hole 2502 a has an apex made as avery small aperture 2502 b having a diameter of several tens ofnano-meters. That is, the clad 2502 has the very small aperture 2502 bformed at a backside thereof. Near-field light P is produced in thevicinity of the very small aperture 2502 b.

The core 2503 is formed by depositing a silicon dioxide on a surface ofthe clad 2502 and along the taper hole 2502 a, and structured byintegrally forming a core straight portion 2503 a in a straight form anda core tip portion 2503 b closing the taper hole 2502 a. The clad 2504is also formed by depositing silicon dioxide on a surface of the core2503.

Meanwhile, the optical waveguide 2501 has, at one end 2501 a, a slantend T1 having a predetermined angle with respect to the core straightportion 2503 a of the core 2503. On the one end T1, a reflection film2505 is formed by a metal film of aluminum (Al), chromium (Cr), gold(Au) or the like or a dielectric multi-layered film. This reflectionfilm 2505 serves to reflect by a reflection surface 2505 a the laserlight La propagating through the core straight portion 2503 a of thecore 2503 leftward in the figure toward the very small aperture 2502 b.

The substrate 2506 is formed of silicon, glass and the like in a plateform, and bonded through an adhesive or the like on a surface of theclad 2504 (optical waveguide 2501). Incidentally, the substrate 2506 andthe clad 2504 (optical waveguide 2501) may be bonded by anodic bonding.Here, the anodic bonding refers to bonding due to ionic bond caused inan boundary surface by applying high voltage to between the substrate2506 and the clad 2504.

In the above structure, where the near-field optical head 2500 isapplied in recording or reading-out by an optical memory, a not-shownrecording medium is placed below the near-field optical head 2500. Therecording medium is a planar substrate, for example, in a disk form andformed of a material applicable with optical recording/reading-out in aphase shift recording scheme, an magneto-optical recording scheme, aphoto-chromic recording scheme or the like, so that informationrecording can be made thereon by locally illuminating light. Also, therecording medium is rotated at high speed during recording/reading-outby a not-shown drive mechanism.

Furthermore, because in this case the near-field light P produced in thevicinity of the very small aperture 2502 b is acted onto the recordingmedium, there is a need of bring the distance between the very smallaperture 2502 b and the recording medium close to nearly a diameter ofthe very small aperture 2502 b. Accordingly, in this example a lubricantis filled between the near-field optical head 2500 and the recordingmedium. By utilizing a surface tension of the lubricant, the distancebetween the near-field optical head 2500 and a recording surface of therecording medium is maintained sufficiently small. Also, the lubricantserves to cause the near-field optical head 2500 to follow up inposition the deflection occurring in a rotary axis direction of therecording medium during high speed rotation. Also, the means of puttingthe distance between the very small aperture 2502 b and the recordingsurface of the recording medium to nearly the diameter of the very smallaperture 2502 b can adopt a flying head scheme used in the conventionalhard disk.

In such a state, the near-field optical head 2500 is controlled by anot-shown near-field optical head control mechanism such that the verysmall aperture 2502 b of the near-field optical head 2500 is positionedto a desired position on a recording surface of the recording medium.Subsequently, when the laser light La emitted from a not-shown laserlight source is incident on the incident end face of the core 2503 ofthe optical waveguide 2501, the laser light La propagates through thecore straight portion 2503 a leftward of the figure and then reflectedtoward the very small aperture 2502 b by the reflection surface 2505 aof the reflection film 2505. Due to this, near-field light P is producedin the vicinity of the very small aperture 2502 b, or in other words ina microscopic space between the very small aperture 2502 b and therecording surface of the recording medium.

The interaction of the near-field light P and the recording mediumsurface causes propagation light to be guided, involving properties ofintensity, phase, etc. dependent upon a recording state on the recordingsurface, to a not-shown light receiving element where converted into anelectric signal. This is sent via a not-shown signal line to a not-shownsignal processing section where a determined of a recording state of aninformation recording point.

The information recording to the recording medium requires to illuminatenear-field light P through the very small aperture 2502 b as describedabove. However, for reading out information recorded on the recordingmedium, it is possible to provide a structure for detecting near-fieldlight at the very small aperture 2502 b or a structure for illuminatingnear-field light and detecting signal light with using a same very smallaperture 2502 b.

Next, a manufacturing method for a near-field optical head 2500according to Embodiment 1 described above will be explained withreference to FIG. 26( a) to FIG. 26( f). First, in FIG. 26( a) a clad2502 is deposited on a surface of a silicon substrate 10 by thetechnique of CVD, sputtering, evaporation or the like stated before suchthat a thin film of silicon dioxide becomes a thickness of 200 nm-50 μm.Then, a photolithography technique is used to form a taper hole 2502 ain the clad 2502.

Specifically, a pin hole having a diameter of 100 nm-1 μm is formed in aresist part applied on a surface of the clad 2502 and then etching ismade by an isotropic dry etch technique. This simultaneously etch theresist part and the clad 2502 in the vicinity of the pin hole at a sameetch rate laterally and vertically. As a result, a taper hole 2502 a ina taper form as shown in the figure is formed in the clad 2502. Here,the taper angle of the taper hole 2502 a can be varied by adjusting anetch selective ratio of the clad 2502 and the resist agent. Also,anisotropic etching can be used to adjust the etch selective ratio ofthe clad 2502 and the resist thereby forming a desired form of a taperhole 2502 a.

Then, a silicon dioxide thin film is deposited and formed to a thicknessof 2 μm-10 μm by a technique similar to the technique of forming theclad 2502 such that it extends along a surface of the clad 2502 andcloses the taper hole 2502 a, thereby forming a core 2503. Next, by asimilar technique a silicon dioxide thin film is deposited and formed toa thickness of 200 nm-50 μm on a surface of the core 2503, therebyforming a clad 2504. This forms an optical waveguide 2500 having theclad 2502, core 2503 and clad 2504 on the surface of the siliconsubstrate 2510.

Here, there are two techniques as a technique to make the refractivityof the core 2503 greater than the refractivity of the clad 2502, 2504.In the case of decreasing the refractivity of the clad 2502, 2504,fluorine (F) may be doped during film-forming the clad. On the otherhand, in the case of increasing the refractivity of the core 2503,germanium (Ge) may be doped during film forming the core. Meanwhile,where a silicon dioxide film is deposited and formed, for example, byCVD or sputtering, the refractivity can be adjusted by adjusting the gaspressure or application voltage during film forming although dependentupon the method of film forming.

Next, in FIG. 26( c), a resist pattern for forming one end surface T1 isformed on the optical waveguide 2501 by the photolithography technique,and then the optical waveguide 2501 in its entirety is taper-etched. Forthe technique of this taper etching, appropriate selection is made fromthe technique listed from item (1) to item (3) given below.

(1) Using a resist pattern as a mask, anisotropic or isotropic etchingis conducted in a state that the etch rate is properly selected for theresist and the silicon dioxide as a structural material for the opticalwaveguide 2501. Due to this, an end surface T1 is formed to an angledependent upon an etch rate difference between the resist material andthe silicon dioxide such that the optical waveguide 2501 at one end 2501a is in a form as shown in the figure.

(2) A resist pattern is formed on a surface of the optical waveguide2501 and then isotropic dry etching is conducted. Due to this, one endsurface T1 is formed by undercut such that one end 2501 a is made to aform as shown in the figure.

(3) A tapered resist pattern is formed on a surface of the opticalwaveguide 2501 in a manner corresponding to one end surface T1. Then,transfer-schemed etching is conducted that anisotropic etching is madein a state the etch rate is properly selected for the silicon dioxide asa structural material of the optical waveguide 2501 and the resist. Thisforms one end surface T1 having a shape of the one end 2501 a as shownin the figure.

Then, in FIG. 26( d), a metal film, dielectric multi-layered film or thelike is formed of aluminum (Al), chromium (Cr) or the like over anentire surface of the optical waveguide 2501 (silicon substrate 2510) asmentioned before by a technique of CVD, sputtering or the like. Next,the films other than the reflection film 2505 shown in the figure areremoved by photolithography and etching. Incidentally, the reflectionfilm 2505 may be deposited and formed in a direction of from left of thefigure in a process to be hereinafter referred to in FIG. 26( e) or FIG.26( f).

Next, in FIG. 26( e), a substrate 2506 is bonded on a surface of theoptical waveguide 2501 (clad 2504) by anodic bonding or adhesivementioned before. As a final process, in FIG. 26( f), wet etching isconducted on the silicon substrate 2510 shown in FIG. 26( e) by usingpotassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH)thereby removing the silicon substrate 2510. Meanwhile, the siliconsubstrate 2510 can be removed by high-speed dry etching. Due to this, anear-field optical head 2500 is manufactured.

As explained above, the near-field optical head according to Embodiment9 uses the optical waveguide in place of a conventional optical fiber,thus being reduced in size and weight. Accordingly, it is possible toeasily follow up a response speed of a feedback system requiringhigh-speed response and ultimately perform recording and reading-outwith high density.

Also, the near-field optical head according to Embodiment 9 describedabove is structured to guide the laser light from a laser light sourceto a position immediately close to the very small aperture. Accordingly,the propagation loss of light can be drastically reduced as compared tothe conventional.

Furthermore, because the near-field optical head according to Embodiment9 as above is formed with the taper hole by isotropic or anisotropic dryetching, the taper hole can be adjusted in its taper angle. Eventually,the adjustment of this taper angle optimizes the efficiency of lighttransmission with a result that the propagation loss of light can bereduced.

Meanwhile, the manufacturing method for a near-field optical headaccording to Embodiment 9 use the technique explained with reference toFIG. 26( a)-FIG. 26( f), i.e. the technique that a clad, a core and aclad are formed in order over the surface of the silicon substrate andthen a substrate is bonded to the optical waveguide. Accordingly, it ispossible to easily form a shape of a protrusion on the optical waveguidecore that has conventionally considered difficult in fabrication.

Embodiment 10

FIG. 27 is a side sectional view showing a structure of a near-fieldoptical head 2700 according to Embodiment 10 of the invention. In FIG.27, the parts corresponding to those of FIG. 25 are put with the samereference numerals to omit explanations thereof. In FIG. 27, areflection film 2721 is newly formed. This reflection film 2721 isformed on the backside 2502 c of a clad 2502. A microscopic diameterhole 2721 a is formed through the reflection film 2721 in a positioncorresponding to the very small aperture 2502 b. This reflection film2721 prevents light from leaking at around the very small aperture 2502b and also serves to prevent, when the light propagating through thecore 2503 leaks as leakage light to the clad 2502, the light from beingilluminated to a recording surface of an optical disk. Meanwhile, italso serves to reflect the propagation light obtained through scatteringof near-field light P toward a not-shown light receiving element.

Also the reflection film 2721 is formed by a technique of CVD,sputtering, evaporation or the like as mentioned before such that ametal film or dielectric multi-layered film is formed of aluminum (Al),chromium (Cr), gold (Au) or the like to a thickness of 100 nm-1 μm on abackside 2502 c of the clad 2502. Furthermore, the microscopic diameterhole 2721 a in the reflection film 2721 is formed by the technique oflithography and etching.

The near-field optical head according to Embodiment 10 is formed withthe reflection film to thereby prevent the core leakage, light fromleaking to an outside of the optical waveguide. Accordingly, it ispossible to effectively narrow a light illumination range on a recordingsurface of a recording medium. Furthermore, the near-field optical headaccording to Embodiment 10 is formed with the reflection film andaccordingly guide the propagation light obtained by scattering ofnear-field light P to the light receiving element, thus improvingdetection sensitivity.

Embodiment 11

FIG. 28 is a side sectional view showing a structure of a near-fieldoptical head 2800 according to Embodiment 11 of the invention. In thisfigure, the corresponding parts to those of FIG. 25 are put with thesame reference numerals. In this figure, the optical waveguide 2501 hasat its one end 2501 a one end surface T2 made in a curved surface. Onthe one end surface T2, a reflection film 2831 is formed of the materialand by technique similar to the reflection film 2505 (see FIG. 25). Thatis, the reflection surface 2831 a of the reflection film 2831 is in acurved surface at the one end surface T2 and hence serves as a concavemirror. That is, the laser light La propagated through the core straightportion 2503 a of the core 2503 is focused by the reflection surface2831 a and reflected toward the very small aperture 2502 b.

The near-field optical head according to Embodiment 11 has thereflection film made in a curved surface and hence can focus laser lightand eventually increase the intensity of near-field light.

Embodiment 12

FIG. 29 is a side sectional view showing a structure of a near-fieldoptical head 2900 according to Embodiment 12 of the invention. In FIG.29, the parts corresponding to those of FIG. 25 are put with the samereference numerals to omit explanation thereof. In FIG. 29, thestructure is not formed with the clad 2504 shown in FIG. 25. That is,the core 2503 is bonded, at a surface, with a substrate 2506 having arefractivity lower than the refractivity of the core 2503 by the anodicbonding or the like mentioned before. The substrate 2506 serves as aclad 2504. Consequently, in FIG. 29 an optical waveguide 2901 isconstituted by the clad 2502, the core 2503 and the substrate 2506.

Accordingly, the near-field optical head according to Embodiment 12 canbe further reduced in size and weight by an amount corresponding to theabsence of a clad as compared to the near-field optical head ofEmbodiment 9. Thus, recording/reading-out is possible with higherdensity.

Although Embodiments 9 to 12 of the invention were described in detailabove, the concrete structure is not limited to those of Embodiments 9to 12 wherein change of design within the range of not departing fromthe gist of the invention is included in the present invention. Forexample, although Embodiments 9 to 12 were explained on a plurality ofstructural examples, the structural examples if properly combined,besides individually practicing them, are also included in theinvention.

Meanwhile, in Embodiments 9 to 12 the light introduced in the opticalwaveguide is not necessarily coherent light but may use light to beemitted as incoherent light from an LED or the like.

Embodiment 13

FIG. 30 is a partial sectional view showing a structure of a near-fieldoptical head according to Embodiment 13. A near-field optical head 3000shown in FIG. 13 is structured by a first substrate 3003 having, in alight introducing portion to introduce laser light emitted from a laserlight source into the near-field optical head 3000, an optical waveguide3002 for propagation with low loss in a direction parallel to a mediasurface, and a light reflection layer 3001 for reflecting the lightpropagated with low loss through the optical waveguide 3002 and direct apropagation direction toward an aperture, a second substrate 3005 havinga lens 3004 designed to focus the laser light directed toward theaperture by a lens effect and align a focused microscopic beam spot tothe aperture, and a third substrate 3009 forming an inverted conical orpyramidal hole 3007 gradually reduced in diameter in a taper form towarda slider surface 3006 opposing to a media and forming a light reflectionfilm 3010 to reflect light upward and increase illumination light to theaperture so that near-field light is produced by illuminating thepropagation light to an apex thereof.

In the first substrate 3003, the optical waveguide 3002 is formed ofquartz-based material or a dielectric material such as polymer, whichmay be structured by a clad 3011, a core 3012 and a clad 3013 as shownin FIG. 30. Here, the optical waveguide 3002 is structured such that thecore 3012 has a refractivity greater than the refractivity of the clad3011 and clad 3013. The core 3012 and the clads 3011, 3013 are formed bydepositing a silicon dioxide film through the technique of CVD (ChemicalVapor Deposition), sputtering or evaporation, thereby enabling to reducethe size of the first substrate 3003. The emission light from thisoptical waveguide 3002 is illuminated to the light reflection layer 3001formed on a slant surface having a predetermined angle so that the lightreflection layer 3001 changes a propagation direction of the light. Inthe case that the first substrate 3003 uses a silicon (100) substrate,anisotropic etching forms, due to (111), a slant surface having a slantdegree of 54.7 degrees on a top surface thereof a light reflection layer3001 is formed of a metal film such as of aluminum, chromium or gold ora dielectric multi-layered film. Due to the light reflection layer 3001,the light illuminated from a semiconductor laser in a direction parallelto a media surface can be illuminated from above to the very smallaperture formed in a plane of a slider. Thus, a near-field optical head3000 is feasible with efficiency of light propagation. Meanwhile, evenwhere as another first substrate 3103 a pattern of an optical waveguide3102 is formed to a further upper stage of a slant surface as shown inFIG. 31, the light propagating in a direction parallel to the mediasurface will propagate toward the very small aperture by the lightreflection layer 3101 formed on the slant surface. Alternatively, asanother first substrate 3203 a quartz material may be formed on a planarsubstrate to conduct etching on the quartz material in a form oftransferring a mask form thereby forming a slant surface having a giventaper angle on which a metal film or the like is laid thereby forming alight reflection layer 3201 (FIG. 32). Alternatively, as another firstsubstrate 3301 a metal film such as of aluminum, gold, silver, copper,titanium or chromium may be laid on a planar substrate by the techniqueof evaporation, sputtering or plating so that a light reflection layer3301 is formed with a taper angle by wet etching great in undercutbeneath a mask or dry etching capable of transferring a mask shape (FIG.33). Alternatively, as shown in FIG. 34 a substrate having an opticalfiber 3402 inserted in a V-shaved groove in the vicinity of a lightreflection layer 3401 may be used as a first substrate 3403. In thiscase, the light emitted from a laser light source is incident on a coreas a part high in refractivity formed inside the fiber 3402. The lightpropagated through the core is illuminated to the light reflection layer3401 through an end face 3404 of the optical fiber inserted in thesubstrate. Where the first substrate uses a silicon (100) substrate asmentioned before, a desired depth of a groove is formed structured bythree slant surfaces with a slant degree of 54.7 degrees by utilizing a(111) plane on which the etch rate is slow. By arranging a circularoptical fiber 3402 in the groove, alignment and positioning is possiblewith accuracy. In the first substrate thus structured (3003, 3103, 3203,3303, 3403), a focusing function may be provided by a concave-formedreflection surface of the light reflection layer. Also, the opticalwaveguide for propagation in a direction parallel to the media surfaceat an incident end surface or emission end surface may have a convexsurface, or the optical waveguide in part have a grating function. Thefocusing function allows for design to match a light spot to the verysmall aperture. By this effect, an increased amount of light can beilluminated to the very small aperture thus realizing high-speedreading-out or recording of information.

The second substrate 3005 uses a substrate having a refractivedistribution different in part thereof. This substrate has arefractivity continuously varying from one surface to the other surfaceof the substrate to have a lens function capable of focusing orcollimating the light incident on the one surface to the other surface.The substrate as this is fabricated by a selective ion exchange methoddescribed later. Alternatively, a substrate having a lens effect due toa lens shape may be used. The lens in form is fabricated by selectinglarge-radius ions in ion exchange to utilize phenomenon that a circularswell is given by the difference in ion radius. Meanwhile, as anothermaking method for a lens form, the resist as a mask for dry etching isformed to a lens shape by a photolithography technique using gray scalemask or immersion mask. The substrate and the resist are simultaneouslyetched under an etch condition that a selective ratio is taken constantfor a dielectric material as a substrate material and the resist,thereby making a desired lens form. The second substrate 3005 having alens function thus properly optically designed is arranged between thefirst substrate 3003 and the third substrate 3009. This makes itpossible to supply an increased amount of light to the very smallaperture 3008 formed in the third substrate 3009. Meanwhile, the secondsubstrate 3005 may use a substrate having in part a grating function ora Fresnel zone plate or a holographic lens. The second substrate 3005thus structured uses a material of dielectric, particularly anSiO₂-based material such as quartz or glass.

The third substrate 3009 uses a silicon substrate. The silicon substrateis formed with a tapered hole 3007 in a manner penetrating through tohave a very small aperture 3008 in a surface on a media side. The holediameter decreases in a direction toward the slider. The propagationlight illuminated from above to the hole travels toward the aperturewhile being reflected at an inside of the taper. This is converted intonear-field light by the very small aperture 3008 formed in the surfaceon the media side and having a microscopic diameter of less than 200nano-meters. The taper is formed by working the silicon substratethrough an anisotropic silicon etching technology. The taper has a lightreflection layer 3010 formed on a surface thereof so that the lightpropagated from above can be reflected to focus an increased amount oflight to the very small aperture. The light reflection film 3010 laid onthe surface of the penetration hole in a manner filling the hole has ahole having a size providing for a size of the very small aperture 3008.In the third substrate 3009, the taper may be structured in a curvedsurface or by multi-staged slant surfaces different in slant degree.Also, the hole may have a part on an inside thereof a material having arefractivity of n=1 or higher or a refractivity distribution or a curvedsurface.

The near-field optical head 3000 according to Embodiment is formed byintegrally bonding the first to third substrates. In bonding, therespective substrates are aligned in position such that an increasedamount of near-field light can be produced by focusing the laser lightreflected by the light reflection layer 3001 formed in the firstsubstrate 3003 by a lens function existing in the second substrate 3005and illuminating the focused light to the very small aperture 3008provided in the third substrate 3009. Also, in order to obtain a desiredintensity of near-field light, optical design is made particularly forthe size or NA of the lens 3004 provided in the second substrate 3005.The bonding between the substrates is made by applying an adhesivebetween the substrates and curing it. Otherwise, direct bonding is madebetween the substrates by an anodic bonding method because the substratematerial uses silicon or glass. Here, anodic bonding refers to bondingdue to ionic bond caused in an interface by inducing high electric fieldbetween silicon and glass or between glasses.

Next, FIG. 35 is an explanatory view showing a manufacturing process fora near-field optical head 3000 of Embodiment 13 shown in FIG. 30.

First, explained is a fabrication method for a first substrate 3003.First, in step S1101 the substrate uses a single crystal siliconsubstrate 3501 having a (100) planar orientation. On this substrate, amasking thermal oxide film 3502 or silicon oxide film is laid by a CVDtechnique or sputtering technique. The mask material may use, besidesthis, silicon nitride or non-alkaline dissolved metal. Next, in stepS1102 a lithography technique is used to open a desired size of a windowin the mask material to expose Si in position to be etched. Thereafterin step S1103 wet etching is made on the silicon substrate 3501 by usingpotassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH)thereby providing a step. Thus, a slant surface 3503 (111) was formedhaving an angle of 54.7 degrees with respect to (100). Subsequently, instep S1104 on a top surface of this slant surface 3503 a lightreflection layer 3504 is formed by a metal film such as of aluminum,silver or gold or a dielectric multi-layered film so that the lightlaterally propagated can be supplied toward the aperture. Furthermore,in step S1105 a material of an optical waveguide is made in a bottom ofthe step by depositing a quartz-based material such as silicon oxide orsilicon nitride and a dielectric material such as polymer of polyimideor polymethacrylate that are turned thereafter into a material for lightpropagation. In the case of silicon oxide as a dielectric material,forming is easy by a sputtering technique, CVD technique or evaporationtechnique. The optical waveguide may be formed by a core 3506 and clads3505, 3507 different in refractivity. To make the refractivity of thecore higher than the refractivity of the clad, germanium may be dopedduring film-forming a core. To make the refractivity of the clad lowerthan the refractivity of the core, fluorine may be doped duringfilm-forming a clad. In such a case, light propagates while beingtotally reflected in the core, thus reducing propagation loss.Subsequently, in step S1106 the optical waveguide 3508 is adjusted inshape by using a photolithography technique and etching. Thephotolithography technology for use in usual semiconductor manufacturingprocess is used to lay a mask material for protection against etching onthe optical waveguide and patterned. Thereafter, the optical waveguidematerial is etched to remove the mask material thereby patterning theoptical waveguide 3508. In this manner, a first substrate 3003 isfabricated. Alternatively, an optical fiber may be inserted in thebottom of the step instead of forming the optical waveguide (FIG. 34).In this case, the substrate is fabricated using the process similar tothat of step S1101 to step S1104 and the fiber is inserted in a V-formedgroove formed by two of (111) having an angle of 54.7 degrees withrespect to (100). Because the angle of the V-groove slant surfaces isconstant, the V-groove can be formed to a desired size by setting adesired size when forming an etch mask shape. As a result, a circularoptical fiber put on the V-groove is determined in position. As aresult, the accuracy in position of light is improved that is beilluminated to the light reflection layer. The fiber is fixed by usingbonding through adhesive or anodic bonding after aligning the fiber inposition.

Meanwhile, in the first substrate shown in FIG. 32 and FIG. 33, lightreflection is done by a slant surface formed by etching to a taper forma dielectric material of metal or silicon oxide or silicon nitride laidon the substrate.

Next, a manufacturing method for a second substrate 3005 will beexplained with FIG. 36. First, in step S1201 a metal film 3602 as a maskmaterial is laid on a glass substrate 3601. Forming is made by vacuumevaporation or sputtering.

Next, in step S1202 a photolithography technique is used to open acircular hole in the metal film 3602 to expose the glass substrate 3601in a position for forming a lens function.

Next, in step S1203 the glass substrate is immersed in a dissolutionsalt to conduct selective ion exchange. The ions to diffuse into theglass substrate intrude in a concentric form through an opening of themask, to have a three-dimensional distribution of concentration. As aresult, the substrate is given a gradient of reflectivity in proportionto the distribution.

Finally, in step S1204 the mask material is stripped off thus forming amicro-lens substrate.

Meanwhile, explanation will be made with FIG. 37 on a manufacturingprocess for a substrate having a lens form formed by using subsequentdry etching.

First, in step S1211 resist 3702 is applied over a glass substrate 3701.

Next, in step S1212 a lens formed resist is made through exposure anddevelopment by lithography using gray scale mask or immersion maskhaving gradation.

Next, in step S1213 the glass substrate is etched under a condition thatthe selective ratio is given constant for the glass and the resist,thereby transferring a resist form onto the glass substrate. When theresist is completely etched on the glass substrate, the substrate iscompleted having the lens form.

Subsequently, explanation will be made with FIG. 38 on a manufacturingmethod for a third substrate 3009. First, in step S1301 the substrateuses a single crystal silicon substrate 3801 having a (100) planarorientation. It is possible to use single crystal silicon with a (110),(111) planar orientation, a dielectric crystal of glass or quartz or asemiconductor crystal such as of GaAs.

Next, in step S1302 a penetration hole 3802 in an inverted pyramid formis formed in the silicon substrate by utilizing anisotropic etchinghaving an etch rate difference depending on a planar orientation of thesingle crystal silicon to provide an aperture at an apex thereof. Athermal oxide film as a mask material is formed on the substrate andpatterned in desired positions by photolithography and etching to exposesilicon. Etching is conducted on the silicon in patterned areas bycrystal axis anisotropic etching with a potassium hydroxide solution ora tetramethylammonium hydroxide solution. At this time, a hole 3802 isformed penetrating through the substrate which is in an inverted pyramidform having a taper surrounded by four surfaces equivalent to the plane(111). The taper angle is given 54.7 degrees to be determined by (111)and (100). The hole diameter decreases as a slider surface isapproached. In a slider surface, a very small aperture is providedhaving one side of 1 μm or smaller. Alternative to immersion in an etchsolution, an inverted conical or pyramidal hole can be formed by usinganisotropic etching, for example, with a reactive ion etching (RIE)apparatus. The mask material may use silicon oxide film or a siliconnitride film in place of the thermal oxide film. Thereafter, the thermaloxide film as a mask material is removed using a mixture solution of ahydrofluoric acid solution and an ammonium fluoride solution.

Next, in step S1303 a light reflection film 3803 is laid on a topsurface of the inverted conical or pyramidal hole. A metal film high inoptical reflectivity such as gold, silver or aluminum is formed on aninside of the hole by vacuum evaporation. The covering method may be byfilm forming using a sputtering technique or an ion plating technique.The provision of the light reflection film 3803, even if the lightilluminated from above hits the slant surface, can guide an increasedamount of light to the aperture by reflection that light. As a result,an increased amount of light can be produced at the aperture. Also, itserves as a shade film against external disturbance light. Also, thelaying of the light reflection film determines a size of the very smallaperture 3804. The aperture formed by etching in the step S1302 isdecreased in size by laying the light reflection film at the inside ofthe hole. Thus, the aperture given by the light reflection film providesa very small aperture 3804 for producing near-field light.

Accordingly, the near-field optical head according to Embodiment 13 campropagate the light emitted from the laser light source to the aperturewith less loss. Particularly, the effect of a lens or a reflectioneffect of the taper near the aperture can supply an increased amount oflight to the very small aperture. Meanwhile, the structure of causinglight to be incident on the head in a direction parallel to a media cankeep a constant distance while approaching a moving media at high speed.As a result, realized is high density of information recording andreading-out at high speed. Also, the reduction in size and price for thehead is realized by the manufacture through a mass-produciblemicro-fabrication process.

Embodiment 14

FIG. 39 is a sectional view showing a structure of a near-field opticalhead 3900 according to Embodiment 14. The near-field optical head 3900of Embodiment 14 has a first substrate 3901 and second substrate 3902similar to the first substrate 3003 and second substrate 3005 shown inEmbodiment 13. However, a third substrate 3903 having a very smallaperture 3904 for producing near-field light is structured having anaperture of a metal film 3906 at a tip of a dielectric conical orpyramidal protrusion 3905 shown in FIG. 39. The conical or pyramidalprotrusion 3905 is formed by forming part of a quartz-based materiallaid on a silicon substrate 3907. However, at this time the height isprovided equivalent, in a surface on a media side of a near-fieldoptical head, for a thickness of a quartz-based material not etched anda tip of the protrusion 3905 formed of the same material. Furthermorethis surface if accessed to a media makes it possible to reduce thedistance between the media and the very small aperture 3904 existing atthe tip of the protrusion 3905, thus illuminating an increased amount oflight produced by the very small aperture 3904 to the media. Also, byadopting a high reflective material such as aluminum, gold or silver fora metal film 3906 formed in the periphery of the protrusion 3905, thelight illuminated from above can be reflected to thereby collect anincreased amount of light to the very small aperture. Incidentally, alarge hole is formed in the silicon substrate 3907 which is directedtoward a bottom of the protrusion 3905 so that light can be incident onthe light-transmissive protrusion 3904. Also, the protrusion 3905 inshape may be in a circular cone or a polygonal pyramid. Alternatively,it may have a slant surface of a protrusion not having a constant angleas in a bell shape.

Meanwhile, a dielectric material high in light transmissivity may beused as another third substrate in Embodiment 14. For example, in thecase of using a substrate of quartz or glass, the substrate is directlyformed without laying a quartz-based material to make a bell-shapedprotrusion similarly to FIG. 39. Then, a metal film or a very smallaperture is formed in a similar fabrication method. When using thesubstrate, the light illuminated to the aperture propagates through aninside of the substrate. Hence, there is no necessity of forming a largehole in the silicon substrate 3907.

The near-field optical head 3900 according to Embodiment is also formedby integrally bonding the first to third substrates similarly toEmbodiment 13. In order to obtain a desired magnitude of near-fieldlight, the respective substrates are formed to meet the optical designconsidering a thickness of the third substrate 3903, a NA, size orthickness of the lens. After properly aligned, bonding is carried out.The method of bonding is similar to Embodiment 13.

Next, an explanatory view showing a manufacturing process for anear-field optical head 3900 of Embodiment 14.

The manufacturing method for a first substrate and second substrate issimilar to the manufacturing method for a near-field optical head ofEmbodiment 13, thus omitting explanation thereof.

The manufacturing method for a third substrate 3903 will be explainedwith FIG. 40. In step S1311 the substrate uses a single crystal siliconsubstrate 3907 with a (100) planar orientation similarly to Embodiment13. It is possible to use a single crystal silicon with a (110), (111)planar orientation, a dielectric crystal of glass or quartz or asemiconductor crystal of GaAs or the like.

Next, in step S1312 a TEOS film 3908 as one kind of silicon oxide islaid by a CVD technique. A dielectric material may be used as othermaterials such as a quartz-based material such as silicon oxide orsilicon nitride high in light transmissivity or a dielectric material ofpolymer such as polyimide or polymethacrylate.

Next, in step S1313 a photolithography technique and chemical etchingare used to form part of the TEOS film 3908 into a conical or pyramidalform. This form will turn into a protrusion 3905 in FIG. 39. An etchmask is formed in a form matched to an etch property usingphotolithography. However, where using dry etching, etching on the TEOSfilm 3908 proceeds while transferring the etch mask pattern.Accordingly, there is a necessity of previously providing a protrusion3905 form in the mask itself. When forming such an etch mask form, anoptical mask having a gradation alike an gray scale mask or immersionmask is used in exposure to the photoresist. The etch mask form featuredby such an optical mask makes possible to form the TEOS film 3908 intoan arbitrary form. Meanwhile, where using a sputtering etch methoddespite in dry etching, the making process is different. The TEOS film3908 is formed beforehand to a columnar or trapezoidal form. Thereafter,by conducting sputter etching, the column or trapezoid is gradually cutat a corner into a tip-sharpened protrusion form. Different from dryetching as above, the use of wet etching if adjusting an etch rate forthe etch mask form and under-etch beneath the mask allows forfabrication of an arbitrary form of a TEOS protrusion. Where the etchmask in form is made in circular, triangular or square, a tip-sharpenedcircular cone, triangular pyramid or square pyramid will be formed. Thisutilizes isotropy in wet etching. The circular, triangular or square inmask form can be easily made by exposure to and development of resistusing a photomask. Also, the under-etch rate if adjusted enables to forma protrusion with an arbitrary taper angle. Where using photoresist as amask, adjustment is made for TEOS film surface roughness, resist kindcoat method or baking temperature to optimize the adherence between theTEOS film and the resist thereby making an arbitrary taper angle. Amixture solution of hydroxide fluoride and ammonium fluoride is used asa wet etchant.

Meanwhile, an FIB (Focused Ion Beam) forming technology may be used toform into a conical or pyramid form that allows for local etching usingsputter principle.

Next, in step S1314 the silicon substrate 3907 at its backside is etchedto form a large hole so that light can be incident to the protrusion3905. A thermal oxide film as an etch mask is patterned by aphotolithography technique to expose silicon. A hole is formed by usingan wet etchant having anisotropy with respect to a silicon crystal axis(potassium hydroxide solution or tetramethylammonium hydroxidesolution). In this case, the etch rate is slow on a plane (111) toprovide an inverted conical or pyramidal hole surrounded by four 54.7degrees slant surfaces. This hole penetrates through the silicon with aresult that the light illuminated at the backside of the silicon canreach a tip of the protrusion 3905.

Next, in step S1315 a metal film 3906 is laid on a surface of the formedTEOS film 3908. A metal film 3906, such as gold, silver or aluminum,high in light reflectivity is formed by vacuum evaporation. The highdeposition rate evaporation condition makes possible to form a film withreduced grain size. The coating method may use a sputter technique or anion plating method in forming a film. By providing a metal film 3906,the illuminated light from above if hits on the protrusion 3905 slantsurface is reflected thereby guiding an increased amount of light to thetip.

Next, in step S1316 the metal film 3906 at the tip of the protrusion3905 is formed into a very small aperture 3904. In the film forming ofthe metal film 3906 in step S1315, the deposition in an obliquedirection of the substrate under a film forming condition high indirectional dependency tends to reduce the thickness at the tip withrespect to the thickness on the protrusion slant surface. The etchingthe metal film 3906 having such a distribution of thickness allows forforming a very small aperture at the tip thereof. Meanwhile, it ispossible as another method to form a mask material having a holecorresponding to a size of a very small aperture at a tip andselectively etch the metal film only in the tip to thereby make a verysmall aperture 3904. In this case, the etch mask can use photoresistformed by spin coating in a state not applied at the tip to expose themetal film. Otherwise, an dielectric material formed by a CVD techniquethin only in the tip may be etched to form a hole in a sizecorresponding to a very small aperture.

Meanwhile, as another forming method a very small aperture may be formedby pressing a smooth-surfaced flat plate formed of a material harderthan a metal film from above the protrusion tip down onto the metal filmto apply a constant load thereby changing the form of the metal film tipinto a flat shape matched to a plate form and exposing the underlyingTEOS film. In this case, the very small aperture can be formed bypressing a tip-sharpened form or spherical form instead of pressing witha flat plate thereby forming the metal film into a form of fit in ashape thereof.

Finally, in step S1317 a dielectric film for a protection film 3909 isformed at a top surface of the metal film 3904. The protection film 3909is formed to a thickness of less than 30 nm. The formation of thedielectric film can suppress the metal film from being decreased inreflectivity by oxidization due to aging or the light reflection filmfrom being stripped off and hence light leak due to contact with amedium. Incidentally, the step S1317 is to be omitted as the case maybe.

Accordingly, the near-field optical head of Embodiment has theaperture-forming material having a reflectivity greater than air inaddition to the effect of Embodiment 13. Thus, light propagation loss isreduced in the vicinity of the aperture and hence the energy densityincreases at the aperture, thereby producing an increased amount ofnear-field light. Meanwhile, the slant surface in the vicinity of theaperture can be set to an arbitrary form to allow for selection to anobject.

Embodiment 15

FIG. 41 is a fragmentary sectional view showing a structure of anear-field optical head according to Embodiment 15. The near-fieldoptical head 4100 of Embodiment 15 has a first substrate 4101 and thirdsubstrate 4103 similar to Embodiment 13 but a second substrate using aball lens 4102. The ball lens 4102 is put at an inside of an invertedconical or pyramidal hole of the third substrate 4103. The lightpropagated through an optical waveguide or light reflection layer formedin the first substrate 4101 is illuminated as converging light to a verysmall aperture formed in the third substrate 4103 by a lens effectcorresponding to a form or reflectivity thereof. The ball lens 4102 inits positioning accuracy is determined by an angle of a slant surfaceand a radius of the sphere. However, because a hole in the thirdsubstrate 4103 is in an inverted square pyramid form having a constantslant degree of 54.7 degrees formed by the plane (111), alignment ispossible with accuracy. Also, the adjustment of the reflectivity of theball lens 4102 and the size of a radius of curvature at the surfaceprovides for illumination of an arbitrary NA of light to the very smallaperture. The material of the ball lens 4102 uses a dielectric materialsuch as a quartz-based material or a polymer material.

Meanwhile, although in the above explanation the third substrate 4103used the substrate as shown in Embodiment 13, the third substrate 3903shown in Embodiment 14 may be used similarly. Also, the first substratemay use a substrate as shown in FIG. 31 to FIG. 33 or a substrate havingan optical fiber inserted in a V-groove as shown in FIG. 34.

The near-field optical head 4100 of Embodiment 15 is formed by bondingthe first substrate 4101 to the third substrate 4103 similarly to thenear-field optical head 3000 of Embodiment 13. The bonding method uses atechnique of bonding through an adhesive or anodic bonding, similarly toEmbodiment 13.

The manufacturing method for a near-field optical head 4100 ofEmbodiment 15 was already explained in Embodiment 13 and Embodiment 14.The method for fabricating a ball lens is omitted herein.

Accordingly, the near-field optical head of Embodiment 15 can obtainhigh positional accuracy by inserting a ball lens in a given-angledslant surface without requiring precise alignment, in addition to theeffects of Embodiment 13 and Embodiment 14. As a result, the process forpositioning the lens can be omitted and the improvement of productionefficiency be desired. Also, the amount of near-field light needed for apurpose is dependent greatly upon a lens NA and thus can be easilysolved by ball lens selection.

Embodiment 16

FIG. 42 is a fragmentary sectional view of showing a structure of anear-field optical head 4200 according to Embodiment 16. The near-fieldoptical head 4200 of Embodiment 16 has a first substrate 4201 and thirdsubstrate 4203 similar to Embodiment 13. However, a second substratehaving a lens function is used and a liquid resin to be set by radiationof a ultraviolet ray is sprayed in spherical fine particles to avicinity of a very small aperture in the third substrate 4203 thusforming into a semi-spherical form to be set by radiating a ultravioletray and making a small-sized lens 4202 having a curved surface toexhibit a lens effect.

Also, although in the above explanation the third substrate 4203 used asubstrate as shown in Embodiment 13, a third substrate 3903 as shown inembodiment 14 may be used in the similar manner. The near-field opticalhead 4300 in this case is shown in FIG. 43. The fine particles to beturned into a lens are sprayed from a hole 4301 formed in a backside ofthe silicon substrate to form a small-sized lens 4302 on a TEOS film4303 existing deep of the hole. Alternatively, where a quartz-basedsubstrate is selected instead of a silicon substrate for a thirdsubstrate, spraying is made to an opposite surface to a surface forminga bell-shaped protrusion to thereby form a small-sized lens. Meanwhile,the first substrate may use a substrate as was shown in FIG. 31 to FIG.33 or a substrate having an optical fiber inserted in a V-groove as wasshown in FIG. 34.

The near-field optical head of Embodiment 16 is formed by bonding thefirst substrate and the third substrate. The bonding method uses atechnology of bonding through an adhesive or anodic bonding similarly tothe bonding method as was explained in Embodiment 13.

The manufacturing method for a near-field optical head of Embodiment 16was already explained in Embodiment 13 and Embodiment 14.

Accordingly, the near-field optical head of Embodiment 16 can form anarbitrary lens by spraying and setting fine particles and hence bemanufactured by a process suited for mass production, in addition to theeffects of Embodiment 13 and Embodiment 14.

Embodiment 17

FIG. 44 is a fragmentary sectional view showing a structure of anear-field optical head 4400 according to Embodiment 17. The near-fieldoptical head 4400 of Embodiment has a first substrate 4401 similar toEmbodiment 13. However, a second substrate and a third substrate aremade as a same substrate wherein on a media-side surface a protrusion4402 and very small aperture 4403 are formed as were formed in the thirdsubstrate of Embodiment 14 and on the opposite surface a glass substratehigh in light transmissivity formed with a refractivity distribution4404, lens form, Fresnel zone plate or holographic lens as were used inthe second substrate of Embodiment 14. A high-transmissive quartz-baseddielectric substrate may be used without limited to the glass substrate.

The lens function, bell-formed protrusion and very small aperture ifformed on one substrate using a series of photolithographic processeseliminates the bonding between the second substrate and the thirdsubstrate as was required in the near-field optical head manufacturedescribed in Embodiment 14. This can avoid a problem with reduction inamount of illumination light from the very small aperture caused due topositional deviation upon boding.

Alternatively, a refractivity distribution is formed in a media-sidesurface of the glass substrate to form a protrusion 4402 and very smallaperture 4403 in the refractivity distribution so that the light focusedby the refractivity distribution can be illuminated to the aperture. Inthis case, a protrusion 4402 is formed having a refractivitydistribution. The near-field optical head having a refractivitydistribution in the protrusion is provided with a lens function in thevicinity of the aperture and can be manufactured by a micro-fabricationprocess using photolithography, improving the accuracy of positioning,exhibiting stable characteristics and being made in a structure suitedfor mass production. Furthermore, a lens function as shown in FIG. 44may be provided in a surface on a first substrate side of the glasssubstrate to provide a structure having a lens function on therespective surfaces of the glass substrate. The glass substrate thushaving a lens function on the opposite surfaces may be formed byperforming a same process on the respective surfaces. Otherwise may beformed by bonding together two glass substrates having a lens functionon one surface. The near-field optical head thus structured with a lensfunction on the opposite surfaces is improved in focusing action owingto a focusing function at two points thereby producing an increasedamount of near-field light through the very small aperture. Furthermore,this can provide focusing by the combination of two lens as compared tothe case that light collection is by one lens for focusing to the verysmall aperture. Thus, manufacture is comparatively easy because ofunnecessity of strict accuracy of positioning between the lenses.

Embodiment 18

FIG. 45 is a fragmentary sectional view showing a structure of anear-field optical head 4500 according to Embodiment 18. The near-fieldoptical head 4500 of Embodiment 18 has, as shown in FIG. 45, opticalelements (optical waveguide 4501, light reflection layer 4502,protrusion 4503, very small aperture 4504) contained in a firstsubstrate, second substrate and third substrate all formed in a surfaceon a media side of a same substrate.

FIG. 46 is an explanatory view showing a manufacturing process for anear-field optical head 4500 in Embodiment 18 shown in FIG. 45.

First, in step S1401, similarly to the first substrate of Embodiment 13,a step is provided in a silicon substrate 4601 to form a lightreflection layer 4602 in the slant surface and in a lower stage anoptical waveguide 4603 for illuminating light to the light reflectionlayer 4602. In also Embodiment 18, a first substrate as shown in FIG. 31to FIG. 33 may be used.

Next, in step S1402 a TEOS film 4604 is laid on a top surface of thelight reflection layer 4602 and optical waveguide 4603 by a CVDtechnique. There is no problem if another dielectric material is used.

Next, in step S1403 the TEOS film having the step in a top surface ispolished and planarized.

Next, in step S1404 a process is conducted that is similar to themanufacturing step S1313 for a near-field optical head of Embodiment 14,to form a conical or pyramidal protrusion 4605 in the TEOS film 4604.

Finally, in step S1405 a process is conducted that is similar to themanufacturing process steps S1315, S1316 for a near-field optical headto thereby form a near-field optical head 4500 of Embodiment 18, shownin FIG. 45, formed with a protrusion 4503 including a very smallaperture 4504, a light reflection layer 4502 and an optical waveguide4501 on a slider-side surface.

The near-field optical head thus structured can shorten the optical pathdistance between an emission end of the optical waveguide 4501 and thevery small aperture 4504. For example, by making approximately 10 μm thethickness of a silicon oxide film to be laid, the distance can be set to10 μm or less. As a result, the beam spot, of propagation light whosediameter increases as the emission end is distant farther can beilluminated as kept small to the very small aperture, thus producing anincreased amount of near-field light. Further, this near-field opticalhead is manufactured by forming a film on a same surface and working thethin film using photolithography without including a bonding process.Accordingly, the positional deviation caused due to bonding, as raisinga problem in Embodiments 13 to 17, is reduced. Thus, it is to beexpected to increase in amount of near-field light produced through thevery small aperture.

INDUSTRIAL APPLICABILITY

As explained above, the near-field optical head of the present inventioncan kept constant at all times a spacing to a media being accessedwithout hindrance to a flexture function of the near-field optical head.While the distance between the very small aperture and the media put inproximity, the surface opposed to the media is a smooth planar surfacehence providing a structure to reduce damage due to contact with therecording medium. Thus, a near-field optical head can be manufacturedwhich is hardly broken and strong, reliable, and high in signal SNratio.

Furthermore, the head is formed therein with an optical waveguide topropagate light in a direction parallel with a media, a function forreflecting the light toward the aperture, a lens function for convergingscattering light, and further a structure for suppressing lightpropagation loss such as a taper shape to focus light to a vicinity ofthe aperture. Accordingly, the focused light with energy density can bepropagated with less loss to the aperture. This produces an increasedamount of stable near-field light from the aperture at all times. Thus,a high density recording and reading-out method is made feasible usinglight which is high in SN ratio and excellent in reliability.

Furthermore, although the intensity of light greatly attenuates in aregion the light propagation member in width is smaller than awavelength, the structure obtained narrowed in this region makes itpossible to produce an increased amount of near-field light from thevery small aperture. As a result of this, a reliable near-field opticalhead can be supplied because of, handling signals high in SN ratio inrecording and reading-out information of a recording medium.

Furthermore, even where the amount of light is low at the laser lightsource, the high efficiency of conversion to near-field light enablessupply of near-field light required for the recording medium.Consequently, the power is saved at the laser light source thussupplying an information reading-out and recording apparatus to bedriven with low power consumption but on low voltage.

Furthermore, against the problem with size increase of an apparatusstructure in light incidence on the near-field optical head from above,the introduction of light to the near-field optical head in a directionparallel with a recording medium reduces the size and thickness of theoverall apparatus. It is possible to follow up winding on a recordingmedium in movement at high speed and hence keep always a constantrelative position to the recording medium. Accordingly, stablenear-field light is to be supplied at all times to the recording medium,enabling supply of a reliable near-field optical head.

Also, the structure having a protrusion protruded from an aperture makesit possible to recording and reading-out information to and frommicroscopic bits with resolution corresponding to a radius of curvatureat a tip of the projection. Also, a spatial distribution of near-fieldlight occurs unique to a protrusion shape. Utilizing this, anillumination range can be determined effectively.

Also, the optical head of the present structure can be manufacturedthrough a micro-machining process using silicon or the like. Also, theincidence of light on the head in a direction parallel with a mediaallows for reduction in size and thickness of the apparatus overall.Simultaneously, realized is cost reduction, product stability and highreliability due to application to a mass production process capable ofbatch processing.

Also, according to a manufacturing method for a near-field optical headof the invention, a very small aperture for producing near-field lightis defined in size and shape by metal film forming, thermal oxidation orion implant on a silicon substrate formed with an aperture greater thana target size. It is therefore possible to manufacture a near-fieldoptical head with higher accuracy and yield as compared to defining asize and shape of a very small aperture by etching or the like.

What is claimed is:
 1. A near-field optical head for recording andreading-out information on and from a recording medium by utilizingnear-field light produced from a very small aperture, the near-fieldoptical head comprising: means defining a tapered hole having an apexthat forms a very small aperture configured to produce near-field light;an optical propagation member for propagating light from a lightincident side thereof along an optical path to the very small aperture,the optical propagation member extending continuously from the lightincident side through the very small aperture and terminating in aprotrusion protruding from the very small aperture; and a lightreflection layer for reflecting light propagating through the opticalpropagation member toward the very small aperture.
 2. A near-fieldoptical head according to claim 1; wherein the protrusion has a conicalor pyramidal shape.
 3. A near-field optical head according to claim 1;wherein the near-field optical head is configured to be maintained at aconstant position relative to the recording medium by a floating forceproduced by air pressure generated from high speed motion of therecording medium.
 4. A near-field head according to claim 1; furthercomprising a slider structure opposed to the recording medium, whereinthe very small aperture is formed in a surface of the slider structure.5. A near-field optical head according to claim 1; wherein the lightreflection layer has a focusing function to focus the light reflectedtoward the very small aperture.
 6. A near-field optical head accordingto claim 1; wherein the light reflection layer is formed on an etchedsurface portion of the near-field optical head that is disposed at anangle relative to the optical path of light propagated through theoptical propagation member.
 7. A near-field optical head according toclaim 1; wherein the means defining a tapered hole comprises a substratehaving the very small aperture formed in a surface thereof opposed tothe recording medium, and wherein the light reflection layer is formedon a surface of the substrate opposite the surface in which is formedthe very small aperture.
 8. A near-field optical head according to claim1; wherein the means defining a tapered hole comprises a substratehaving the very small aperture formed in a surface thereof opposed tothe recording medium; and wherein the light reflection layer is formedon the surface of the substrate in which is formed the very smallaperture.
 9. A near-field optical head according to claim 1; wherein theoptical propagation member has, along the optical path, two or morestages of slant surfaces having different angles of slant.
 10. Anear-field optical head according to claim 1; wherein the tapered holehas a conical or a pyramidal shape.
 11. A near-field optical headaccording to claim 10; wherein the protrusion has a conical or apyramidal shape.
 12. A near-field optical head according to claim 1;wherein both the tapered hole and the protrusion have a conical or apyramidal shape.
 13. A near-field optical head according to claim 1;wherein the optical propagation member is made of dielectric material.14. A near-field optical head according to claim 1; wherein the meansdefining a tapered hole comprises a substrate having the very smallaperture formed therein, the light reflection layer is formed on thesubstrate, and the optical propagation member is formed on the lightreflection layer.
 15. A near-field optical head according to claim 14;wherein the optical propagation member comprises a dielectric layerformed on the light reflection layer.
 16. A near-field optical headaccording to claim 1; wherein the protrusion protrudes from the verysmall aperture less than 200 nm.